Isuzu Trooper Limited 1997 - 1997 ENGINE PERFORMANCE Self-Diagnostics

Isuzu Trooper Limited 1997 - INTRODUCTION

NOTE:

The CHECK ENGINE light is now referred to as Malfunction Indicator Light (MIL). The MIL is displayed in instrument cluster as CHECK ENGINE.

If no faults were found while performing Basic Diagnostic Procedures, proceed with self-diagnostics. If no Diagnostic Trouble Codes (DTCs) are present after entering self-diagnostics, proceed to TESTS W/O CODES article for diagnosis by symptoms.

Isuzu Trooper Limited 1997 - SYSTEM DESCRIPTION

The PCM monitors engine operation. It also contains a self-diagnostic system which stores Diagnostic Trouble Codes (DTCs) and compares them to On-Board Diagnostics Generation II (OBD-II) standards.

The goal of OBD-II regulation is to provide vehicle with an on-board diagnostic system which is capable of continuously monitoring the efficiency of emission control systems, and to improve diagnosis and repair when system failures occur.

The Federal Test Procedure (FTP) sets maximum allowable emission standards. A Malfunction Indicator Light (MIL) must illuminate if a system or component either fails or deteriorates to a point where the vehicles emissions could rise above 1 1/2 times FTP standards.

DTCs may only be retrieved using an On-Board Diagnostic (OBD-II) scan tester.

Isuzu Trooper Limited 1997 - TRIP DETECTION LOGIC

Generation II data streams are prioritized. When two messages attempt to establish communications on a data line at the same time, only the message with higher priority will continue. A new segment of the software called the Diagnostic Executive coordinates the protocol for recording and displaying diagnostic procedures.

After engine has reached normal operating temperature, Diagnostic Executive checks if On Board Diagnostic Tests have been completed since last ignition cycle. It checks if tests have passed during current ignition cycle. Checks if fault identified by diagnostic tests is currently active. It also checks if fault identified has been active during current ignition cycle and what operating conditions were present at the time of failure.

Each test is separated in to four types:

• Type A
  
  Turns the MIL on the first time an emission related failure occurs. The MIL will FLASH at a rate of once per second to alert the operator of potentially damaging levels of misfire, such that could destroy the catalytic converter.

• Type B
  
  Will only turn MIL on if an emission related condition occurs during two consecutive driving cycles. Conditions such as incorrect fuel trim will be stored in the Freez-Frame data until the fault is detected a second time. If the fault is not detected during three consecutive driving cycles, the MIL light will be turned off.

• Type C
  
  This is a non-emission related type and will not activate the MIL. It will turn ON a Check Transmission service light, or other non MIL service reminder light.

• Type D
  
  Is non-emission related, will not turn the MIL or service light, but will store DTCs of faults present.

Isuzu Trooper Limited 1997 - SELF-DIAGNOSTIC SYSTEM HARD FAILURES

Hard failures cause Malfunction Indicator Light (MIL) to glow and remain on until problem is repaired. If light comes on and remains on (light may flash) during vehicle operation, cause of malfunction must be determined using diagnostic (code) charts. See DIAGNOSTIC TROUBLE CODE (DTC) IDENTIFICATION . If a sensor fails, Powertrain Control Module (PCM) will use a substitute value in its calculations to continue engine operation. In this condition, commonly known as limp-in mode, vehicle runs but driveability will not be optimum.

Isuzu Trooper Limited 1997 - INTERMITTENT FAILURES

Intermittent failures may cause MIL to flicker or glow and go out after intermittent fault goes away. However, corresponding DTC will be retained in PCM memory. If related fault does not reoccur within a certain time frame, related DTC will be erased from PCM memory. Intermittent failures may be caused by a sensor, connector or wiring related problems. See INTERMITTENTS in TESTS W/O CODES article.

Isuzu Trooper Limited 1997 - FREEZE-FRAME DATA

According to the 1996 government regulations, engine operating conditions where MIL is illuminated must be recorded. This record, called freeze frame data, is a snap shot of the driving conditions, that is recorded on the PCM freeze frame buffer and is constantly updated with the most current information.

Freeze frame data can only be overwritten with misfire or fuel trim malfunction data. The data can only be erased by clearing associated history DTCs.

Isuzu Trooper Limited 1997 - DATA LINK CONNECTOR LOCATION

Located at lower left side of instrument panel, behind a small cover.

Isuzu Trooper Limited 1997 - RETRIEVING CODES

NOTE:

Codes can be retrieved using a scan tester. Trouble codes are referred to as DTCs.

1. Code retrieval starts with diagnostic circuit check. See ON-BOARD DIAGNOSTIC II (OBD-II) SYSTEM CHECK . MIL will come on when ignition is on and engine is not running. When engine is started, MIL should go off. If light remains on while engine is running, a DTC is present.
2. If light does not come on with ignition on and engine off, inspect MIL circuit before continuing. If MIL fails to operate, see ON-BOARD DIAGNOSTIC II (OBD-II) SYSTEM CHECK .
3. To retrieve codes, install scan tool. Select MIL dash lamp control and command the MIL OFF. Ensure MIL light is off and attempt to start engine. If vehicle does not start, go to vehicle NO-START tests. See appropriate BASIC DIAGNOSTIC PROCEDURES article.

Isuzu Trooper Limited 1997 - CLEARING CODES

1. After repairs are performed, clear PCM memory of all stored codes. Ensure ignition is off. To clear codes, use diagnostic scan tool "clear DTCs" or "clear info" function. Follow instructions supplied by tool manufacturer, when clearing DTCs.
2. DTCs can also be cleared by disconnecting any PCM power source or negative battery cable for at least 30 seconds. However, if disconnecting battery remember that other memory functions (clock, radio, etc.) will need to be reset.

Isuzu Trooper Limited 1997 - PCM REPROGRAM PROCEDURE

If PCM requires replacement PCM must be reprogrammed using a Tech I or other OBD II compatible scan tool.

Isuzu Trooper Limited 1997 - PCM LOCATION

PCM is located in passenger compartment below center console.

Isuzu Trooper Limited 1997 - ON-BOARD DIAGNOSTIC II (OBD-II) SYSTEM CHECK

The On-Board Diagnostic II (OBD-II) System Check is the starting point for any driveability complaint diagnosis. Before any DTC(s) are retrieved, perform a visual underhood inspection checking battery and grounds for clean and tight connections. Check for poor connections or damage to wiring harness and electrical connectors. Check for corroded terminals or corrosion build-up on any connection. Repair as necessary. The OBD-II system check is an organized approach to identifying problems created by an electronic engine control system malfunction.

Use of Tech 2 scan tool is required to perform ON-BOARD DIAGNOSTIC II (OBD-II) SYSTEM CHECK. To reprogram EEPROM or to program PCM after it has been replaced, see COMPUTER RELEARN PROCEDURES article in GENERAL INFORMATION section.

NOTE:

To identify component terminals and wire colors, see appropriate wiring diagram in WIRING DIAGRAMS article.

NOTE:

Perform all voltage tests with a Digital Volt-Ohmmeter (DVOM) with a minimum 10-megohm impedance, unless stated otherwise in test procedure.

1. Turn ignition on with engine off. Verify Malfunction Indicator Light (MIL) is on. If MIL is on, go to next step. If MIL is not on, go to BASIC TESTING article.
2. Turn ignition off. Install Tech 2 scan tool. Turn ignition on. If scan tool displays PCM data, go to next step. If scan tool does not display PCM data, verify scan tool is properly installed. If scan tool is properly installed, go to step 8 .
3. Using scan tool, command MIL OFF. If MIL turns off, go to next step. If MIL does not turn off, go to BASIC TESTING article.
4. Start engine. If engine starts and continues to run, go to next step. If engine will not run, go to BASIC TESTING article.
5. Using scan tool, check if any DTCs have been set. If any DTCs are set, go to next step. If no DTCs are set, go to step 7 .
6. Are 2 or more of the following DTC(s) stored?
   • P0107
   • P0108
   • P0113
   • P0118
   • P0122
   • P0123
   • P0712
   • P1392
   • P1406

   If 2 or more of these codes are stored, go to BASIC TESTING article. If a single DTC is stored, go to appropriate DTC test under DIAGNOSTIC TESTS in appropriate TESTS W/CODES article.

7. Compare PCM data values displayed to typical engine scan data values. See appropriate SCAN TOOL DATA VALUES table under PIN VOLTAGE (VALUE) TESTS in PIN VOLTAGE CHARTS article. If values displayed are normal or close to typical values, OBD-II system check is complete. If driveability problem still exists, go to TESTS W/O CODES article. If values are not correct, go to I - SYSTEM & COMPONENT TESTS article.
8. Turn ignition off. Disconnect PCM connectors. Turn ignition on with engine off. Check for open or short in class 2 data circuit (Orange/Green wire) between Data Link Connector (DLC) terminal No. 2 and PCM 32-pin connector C-1, terminal B13. Also check for open or short in ignition feed circuit (Green/White wire) between DLC terminal No. 16 and dash fuse box. Also check for open in ground circuit (Black wire) to DLC terminal No. 4. If problem is found, repair as necessary and return to step 2 . If no problem is found, go to next step.
9. Attempt to reprogram EEPROM. Programming PCM/EEPROM requires the use of a scan tool and special manufacturer equipment. Attempt to display PCM data on scan tool. If data is now displayed, return to step 2 . If data is not displayed, go to next step.
10. Replace PCM. Program PCM. After repair, return to step 2 .

Isuzu Trooper Limited 1997 - DIAGNOSTIC TROUBLE CODE DEFINITIONS

NOTE:

If any DTCs not listed here are displayed by a scan tool, the scan tool data may be faulty. Notify the scan tool manufacturer of any DTCs displayed that are not included in the following.

Isuzu Trooper Limited 1997 DIAGNOSTIC TROUBLE CODE (DTC) IDENTIFICATION

DTC Type	Component/System	Most Likely Cause
P0101 /B	MAF Sensor Circuit Range/ Performance Problem	MAF Sensor
P0102 /A	MAF Sensor Circuit Low Frequency	Open/Short, MAF Sensor Or PCM
P0103 /A	MAF Sensor Circuit High Frequency	Open/Short, MAF Sensor Or PCM
P0106 /A	MAP Sensor Circuit Range/ Performance Problem	MAP Sensor
P0107 /A	MAP Sensor Circuit Low Frequency	Open/Short, MAP Sensor Or PCM
P0108 /A	MAP Sensor Circuit High Frequency	Open, MAP Sensor Or PCM
P0112 /A	IAT Sensor Circuit Low Frequency	Short, IAT Sensor Or PCM
P0113 /A	IAT Sensor Circuit High Frequency	Open, IAT Sensor Or PCM
P0117 /A	ECT Sensor Circuit Low Frequency	Short, ECT Sensor Or PCM
P0118 /A	ECT Sensor Circuit High Frequency	Open, ECT Sensor Or PCM
P0121 /A	TP Sensor Circuit Range/ Performance Problem	TP Sensor Or PCM
P0122 /A	TP Sensor Circuit Low Frequency	Open/Short, TP Sensor Or PCM
P0123 /A	TP Sensor Circuit High Frequency	Open Circuit, TP Sensor Or PCM
P0125 /B	ECT Sensor Circuit Excessive Warm-Up Time To Closed Loop	Cooling System, ECT Or PCM
P0131 /A	Bank 1 Primary HO2S Circuit Low Voltage	Short, HO2S Sensor, Fuel Supply Or PCM
P0132 /A	Bank 1 Primary HO2S Circuit High Voltage	Open, HO2S Sensor Or PCM
P0133 /B	Bank 1 Primary HO2S Slow Response	HO2S Sensor Or Exhaust System
P0134 /A	Bank 1 Primary HO2S Insufficient Activity	Poor Connections, HO2S Sensor Or PCM
P0135 /B	Bank 1 Primary HO2S Heater Circuit Malfunction	Open/Short Or PCM
P0137 /A	Bank 1 Secondary HO2S Circuit Low Voltage	Short, HO2S Or PCM
P0138 /A	Bank 1 Secondary HO2S Circuit High Voltage	Open, HO2S Or PCM
P0140 /A	Bank 1 Secondary HO2S Circuit Insufficient Activity	Short In Circuit, HO2S Or PCM
P0141 /B	Bank 1 Secondary HO2S Circuit Malfunction	Open/Short In Heater Circuit Or PCM
P0143 /A	Bank 1 Secondary HO2S Low Voltage (M/T Only)	Short, HO2S Or PCM
P0144 /A	Bank 1 Secondary HO2S High Voltage (M/T Only)	Open/Short, HO2S Or PCM
P0146 /A	Bank 1 Secondary HO2S Insufficient Activity (M/T Only)	Short, HO2S Or PCM
P0147 /B	Bank 1 Secondary HO2S Heater Circuit (M/T Only)	Short Or HO2S
P0151 /A	Bank 2 Secondary HO2S Circuit Low Voltage	Short Or PCM
P0152 /A	Bank 2 Secondary HO2S Circuit High Voltage	Short, HO2S Or PCM
P0153 /B	Bank 2 Secondary HO2S Circuit Slow Response	Open/Short, HO2S Contamination Or PCM
P0154 /A	Bank 2 Secondary HO2S Insufficient Activity	HO2S Or PCM
P0155 /B	Bank 2 Secondary HO2S Heater Circuit	Short Or HO2S
P0157 /A	Bank 2 Secondary HO2S Circuit Low Voltage (A/T Only)	Short Or PCM
P0158 /A	Bank 2 Secondary HO2S Circuit High Voltage (A/T Only)	Short, HO2S Or PCM
P0160 /A	Bank 2 Secondary HO2S Circuit Insufficient Activity (A/T Only)	Short, HO2S Or PCM
P0161 /B	Bank 2 Secondary HO2S Heater Circuit Malfunction (A/T Only)	Short Or HO2S
P0171 /B	Bank 1 System Too Lean	Fuel Supply/ Contamination, Primary HO2S, MAP, Leaking Exhaust Or Valve Clearance
P0172 /B	Bank 1 System Too Rich	Fule Supply, Primary HO2S, MAP Sensor, Fuel Contamination Or Valve Clearance
P0174 /B	Bank 2 System Too Lean	Air Intake System, MAF Sensor, Fuel Supply Or Exhaust System
P0175 /B	Bank 2 System Too Rich	Air Intake System, MAF Sensor, Fuel Supply Or TP Sensor
P0200/A	Injector Control Circuit	Open/Short, Faulty Injector Or PCM
P0201 /A	Injector No. 1 Circuit Malfunction	Open/Short Or PCM
P0202 /A	Injector No. 2 Circuit Malfunction	Open/Short Or PCM
P0203 /A	Injector No. 3 Circuit Malfunction	Open/Short Or PCM
P0204 /A	Injector No. 4 Circuit Malfunction	Open/Short Or PCM
P0205 /A	Injector No. 5 Circuit Malfunction	Open/Short Or PCM
P0206 /A	Injector No. 6 Circuit Malfunction	Open/Short Or PCM
P0218/D	Transmission High Temp. Condition(A/T Only)	Miscellaneous
P0300 /B	Random Misfire Detected	Ignition System, Fuel Supply, MAP Sensor, EGR System Detected System, IAC Valve Or Contaminated Fuel
P0301 /B	Cylinder No. 1 Misfire Detected	Miscellaneous
P0302 /B	Cylinder No. 2 Misfire Detected	Miscellaneous
P0303 /B	Cylinder No. 3 Misfire Detected	Miscellaneous
P0304 /B	Cylinder No. 4 Misfire Detected	Miscellaneous
P0305 /B	Cylinder No. 5 Misfire Detected	Miscellaneous
P0306 /B	Cylinder No. 6 Misfire Detected	Miscellaneous
P0325 /A	Knock Sensor (KS) Circuit Malfunction	PCM
P0327 /A	KS Circuit	Open/Short, KS Or PCM
P0335/A	Crankshaft Position (CKP) Sensor Circuit Malfunction	CKP Sensor, Circuit Or PCM
P0336 /B	CKP Sensor Range/Performance	CKP Sensor, Valve Timing Or Timing Belt Skipped Teeth
P0337 /B	CKP Circuit Low Frequency	Open/Short, CKP Sensor Or PCM
P0338/A	CKP Sensor High Frequency	CKP Sensor Circuit Or VCM
P0339/A	CKP Sensor Circuit Intermittent	CKP Sensor, CKP Sensor Circuit Or VCM
P0340/A	CMP Sensor Circuit	CMP Sensor, CMP Sensor Circuit Or VCM
P0341 /A	CMP Circuit Performance	Open/Short, CMP Sensor, Faulty Or Missing CMP Magnet OR PCM
P0342 /A	CMP Sensor Low Frequency	CMP Sensor/Magnet Or PCM
P0351 /A	Ignition Coil 1 Circuit	Ignition Control Module (ICM), Open/ Short Or PCM
P0352 /A	Ignition Coil 2 Circuit	Miscellaneous
P0353 /A	Ignition Coil 3 Circuit	Miscellaneous
P0354 /A	Ignition Coil 4 Circuit	Miscellaneous
P0355 /A	Ignition Coil 5 Circuit	Miscellaneous
P0356 /A	Ignition Coil 6 Circuit	Miscellaneous
P0401 /A	Insufficient EGR Flow Detected	EGR Valve Or Line
P0404/A	EGR Valve Pintle Position Open	EGR Valve, EGR Valve Circuit Or PCM
P0405/A	EGR Valve Sensor Signal Low	EGR Valve, EGR Valve Circuit Or PCM
P0420 /A	Bank 1 Catalyst System Efficiency Below Threshold	Catalytic Converter Or Secondary HO2S
P0430 /A	Bank 2 Catalyst System Efficiency Below Threshold	(A/T Only) Catalytic Converter Or Secondary HO2S
P0440 /A	EVAP System	Canister Purge Valve,Vent Solenoid Or Hoses
P0441/B	Evaporative Emission Control System, Incorrect Purge Flow	EVAP Canister, Vacuum Switch, Purge Solenoid Or PCM
P0442 /A	EVAP Small Leak Detected	Vent Solenoid, Fuel Cap Or Lines
P0446 /A	EVAP Canister Vent Blocked	Vent Solenoid Or Canister
P0460/D	EVAP Fuel Level Sensor Circuit	Miscellaneous
P0461 /D	Fuel Level Sensor Circuit Performance	Fuel Level Sensor/ Circuit Or PCM/VCM
P0462 /D	Fuel Level Sensor Circuit Low Voltage	Fuel LevelSensor/ Circuit Or PCM/VCM
P0463 /D	Fuel Level Sensor Circuit High Voltage	Fuel Level Sensor/ Circuit Or PCM/VCM
P0500/A	Vehicle Speed Sensor (VSS) Circuit	VSS, Circuit Or PCM
P0501/A	Vehicle Speed Sensor (VSS) Circuit Range/Performance	VSS, Circuit Or PCM
P0502 /A	VSS Circuit Low Frequency	Open/Short, VSS Or PCM
P0506 /B	Idle Control System Low RPM	IAC Valve Or PCM
P0507 /B	Idle Control System High RPM	IAC Valve Or PCM
P0530/D	A/C Refrigerant Pressure Sensor Circuit	Open, A/C Refrigerant Pressure Sensor Or PCM
P0560/D	System Voltage Malfunction (A/T Only)	Miscellaneous
P0562 /D	System Voltage Low	Open Or PCM
P0563 /D	System Voltage High	PCM
P0601 /A	Powertrain Control module (PCM) Memory Check Sum Error	PCM
P0602/D	PCM Not Programmed	PCM
P0704/B	Clutch Switch Circuit	Clutch Switch/ Circuit Or VCM
P0705/D	Transmission Range Sensor Circuit Malfunction	Miscellaneous
P0706/D	Transmission Range Sensor Rationality	Miscellaneous
P0712/D	Transmission Fluid Temperature Low Voltage	Miscellaneous
P0713/D	Transmission Fluid Temperature High Voltage	Miscellaneous
P0719/D	Brake Switch Circuit Low	Miscellaneous
P0722/A	Output Speed Sensor Circuit No Signal	Miscellaneous
P0723/A	Output speed Sensor Circuit Intermittent Signal	Miscellaneous
P0724/D	Brake Switch Circuit High	Miscellaneous
P0730/C	Wont Shift Between 1/2nd, 2/3rd, 2/4th. Stuck in 1st Or 4th gears (A/T)	Faulty Shift Control System
P0742/A	Torque Converter Clutch Circuit Stuck On	Miscellaneous
P0748/C	Transmission Pressure Control Solenoid Electrical Circuit Fault	Miscellaneous
P0751/B	Transmission Shift Solenoid "A" Performance Or Stuck Off (A/T Only)	Miscellaneous
P0753/A	Transmission Shift Solenoid "A" - Electrical Circuit Fault	Open/Short In Circuit Or Faulty Solenoid
P0756/B	Transmission Shift Solenoid "B" Performance Stuck Off (A/T Only)	Miscellaneous
P0758/A	Transmission Shift Solenoid "B" - Electrical Circuit Fault	Open/Short In Circuit Or Faulty Solenoid
P1106 /D	Manifold Absolute Pressure (MAP) Circuit Intermittent High Voltage	Open/Short In Circuit
P1107 /D	MAP/Barometric Pressure Circuit Low Voltage	Intermittent Open/ Short Or PCM
P1111 /D	Intake Air Temperature (IAT) Circuit Intermittent High Voltage	Poor Ground Or Open Circuit
P1112 /D	IAT Circuit Intermittent Low Voltage	Short In Circuit
P1114 /D	Engine Coolant Temperature (ECT) Circuit Intermittent Low Voltage	Intermittent Short
P1115 /D	ECT Circuit Intermittent High Voltage	Poor PCM Ground Or Open
P1121 /D	Throttle Position (TP) Circuit Intermittent High Voltage	Open/Short Or Poor Ground In Circuit
P1122 /D	TP Circuit Intermittent Low Voltage	Open/Short Or Poor Ground In Circuit
P1133 /B	Bank 1 Primary HO2S Circuit Insufficient Switching	Exhaust Leak, Short In Circuit, HO2S Or PCM
P1134 /B	Bank 1 Primary HO2S Circuit Transition Time Ratio	Exhaust Leak, Open/ Short In Circuit, HO2S Or PCM
P1153 /B	Bank 2 Primary HO2S Circuit Insufficient Switching	Exhaust Leak, Short In Circuit, HO2S Or PCM
P1154 /B	Bank 2 Primary HO2S Circuit Transition Time Ratio	Exhaust Leak, Open/ Short In Circuit HO2S Or PCM
P1171 /A	Fuel System Lean During Acceleration	Fuel Pressure, Incorrect Fuel Or Hot Fuel
P1336	CKP System Variation Not Learned	Miscellaneous
P1345	CMP/CKP Sensor Correlation	Mechinical Problem
P1351	Ignition Control Circuit High Voltage	Ignition Module/ Circuit Or VCM
P1361	Top Dead Center Sensor Intermittent Interruption	TDC Sensor
P1380/A	ABS DTC Detected Rough Road Data Unusable	PCM
P1381/A	CPS Intermittent Interruption	CYP Sensor
P1390 /D	G-Sensor Circuit Intermittent Low Voltage	Open/Short
P1391 /B	G-Sensor Circuit Performance	G-Sensor Or PCM
P1392 /A	G-Sensor Circuit Low Voltage	PCM
P1393 /A	G-Sensor Circuit High Voltage	Poor Grounds, G-Sensor Or PCM
P1394 /D	G-Sensor Circuit Intermittent High Voltage	Poor Ground, MAP Or G-Sensor
P1404	EGR Valve Closed Pintle Position	EGR Valve/Circuit Or PCM
P1406 /A	Exhaust Gas Recirculation (EGR) Valve Pintle Position Circuit	Open/Short, EGR Or PCM
P1441 /B	Evaporative Emission (EVAP) System Flow During Non-Purge	Short, PCM, EVAP Purge Solenoid Or EVAP Vacuum Switch
P1442/B	EVAP System Vacuum Switch Circuit	Open/Short, PCM Or EVAP Vacuum Switch
P1508 /B	Idle Control System Low RPM	IAC Valve Circuit Or PCM
P1509 /B	Idle Control System High RPM	Vacuume Leaks, IAC Circuit Or PCM
P1520	Park Neutral Position (PNP) Switch Circuit	PNP Switch Or Circuit
P1601	Serial Communication Malfunction	PCM Or Data Bus
P1602	EBCM/EBTCM Serial Data Circuit	PCM Or Data Bus
P1607	PCM Internal Circuit Failure "A"	PCM
P1618 /A	Serial Peripheral Interface. PCM Interprocessor Communication Error	PCM
P1621	PCM Memory Performance	PCM
P1640 /D	ODM "A" Fault	Open in Ignition Circuit Or PCM

Isuzu Trooper Limited 1997 - DIAGNOSTIC TESTS

NOTE:

See PIN VOLTAGE CHARTS and WIRING DIAGRAMS articles for PCM harness connector, wire terminal and wire color identification.

NOTE:

If PCM requires replacement, PCM must be reprogrammed using a Tech 1 or other OBD-II compatible scan tool.

Isuzu Trooper Limited 1997 - DTC P0101 - MASS AIRFLOW (MAF) SENSOR CIRCUIT PERFORMANCE Diagnostic Aids

An intermittent problem can be caused by misrouted harness, rubbed-through wire insulation or broken wire inside insulation. Also, check for vacuum or PCV system leaks, incorrect PCV valve, engine oil dipstick not fully seated or engine oil filler cap loose or missing.

1. Perform On-Board Diagnostic (OBD) System Check. See BASIC TESTING article. Go to next step.
2. Turn ignition on, with engine off. Using scan tool, select MAP from ENGINE 1 DATA LIST function. If MAP value is more than 85 kPa (sea level), go to next step. If not, go to step 19).
3. Remove MAP sensor from intake manifold, leaving harness connector connected. Install a hand-held vacuum pump to MAP sensor. Observe MAP sensor reading on scan tool while applying vacuum. Each one in. Hg applied should result in 3-4 kPa drop. Value should change smoothly with each increase in vacuum. If MAP value changed smoothly without any erratic reading, go to step 19). If reading is erratic, go to next step.
4. Apply up to 20 in. Hg to MAP sensor. If MAP sensor reading is 34 kPa or less, go to next step. If not, go to step 19).
5. Remove vacuum source from MAP sensor. If MAP sensor reading returns to original value, go to next step. If reading does not return to original value, go to step 19).
6. Turn ignition on, with engine off. Using scan tool, review FREEZE FRAME and/or FAILURE RECORDS data and note parameters. Turn ignition off for about 15 seconds. Start engine and operate vehicle within conditions required for this diagnostic to run, and as close to conditions recorded in FREEZE FRAME/FAILURE RECORDS as possible. Select DTC function and enter DTC P0101. If scan tool indicates that this test failed this ignition, go to next step. If scan tool does not indicate that this test failed this ignition, see DIAGNOSTIC AIDS .
7. Check for blockage in MAF sensor inlet screen, intake manifold leak, vacuum leak at throttle body, leak at EGR valve flange and pipes, or faulty PCV valve. Repair or replace as necessary. After repairs, go to step 21). If no problem is found, go to next step.
8. Turn ignition off. Disconnect MAF sensor connector. Turn ignition on, with engine off. Using DVOM, check voltage between MAF sensor signal circuit and ground. If DVOM reads about 5 volts, go to next step. If not, go to step 10).
9. Connect test light between MAF sensor ignition feed circuit and ground circuit at sensor harness connector. If test light illuminates, go to step 13). If test light does not illuminate, go to step 12).
10. If voltage is less than 4.5 volts, go to step 14). If voltage is more than 4.5 volts, go to next step.
11. Turn ignition off. Disconnect PCM harness connector. Turn ignition on, with engine off. Using a DVOM, check voltage between MAF sensor signal circuit and ground. If voltage is zero volts, go to step 20). If not, go to step 17).
12. Connect a test light between MAF sensor ignition feed circuit and chassis ground. If test light illuminates, go to step 15). If test light does not illuminate, go to step 16).
13. Check for poor connection at MAF sensor harness terminal. Repair or replace as necessary. After repairs, go to step 21). If connection is okay, go to step 18).
14. Check MAF signal circuit between PCM and MAF sensor for open, short to ground or short to MAF ground circuit. Repair open or shorted circuit. After repairs, go to step 21). If circuits are okay, go to step 20).
15. Locate and repair open in ground circuit to MAF sensor. After repairs, go to step 21).
16. Locate and repair open in ignition feed circuit to MAF sensor. After repairs, go to step 21).
17. Locate and repair short to voltage in MAF sensor signal circuit. After repairs, go to step 21).
18. Replace MAF sensor. After replacing MAF sensor, go to step 21).
19. Replace MAP sensor. After replacing MAP sensor, go to step 21).
20. Replace PCM. Program replacement PCM using required equipment. After replacing PCM, go to next step.
21. Using scan tool, select DTC, CLEAR INFO. Start and warm engine to normal operating temperature. Select SPECIFIC DTC, then enter DTC P0101. Operate vehicle within conditions for setting this DTC. If scan tool indicates that this test ran and passed, go to next step. If scan tool does not indicate that this test ran and passed, repeat step 2).
22. Using scan tool, select CAPTURE INFO, REVIEW INFO function. If any undiagnosed DTC(s) are displayed, go to applicable DTC test.

Isuzu Trooper Limited 1997 - DTC P0102 - MASS AIRFLOW (MAF) SENSOR CIRCUIT/LOW FREQUENCY Diagnostic Aids

An intermittent problem can be caused by misrouted harness, rubbed-through wire insulation or broken wire inside insulation. Also, a plugged or restricted air intake can cause intermittent failure.

1. Perform On-Board Diagnostic (OBD) System Check. See BASIC TESTING article. Go to next step.
2. Start engine and allow it to reach normal operating temperature. With engine at idle, monitor MAF FREQUENCY parameter on scan tool. If display is less than 1000 Hz, go to next step. If display is 1000 Hz or greater, go to step 5).
3. With ignition on and engine off, review and record FAILURE RECORDS data on scan tool. Operate vehicle within FAILURE RECORDS conditions. If DTC P0102 is set, go to next step. If DTC P0102 is not set, see DIAGNOSTIC AIDS .
4. Turn ignition off. Disconnect MAF sensor harness connector. Turn ignition on. Using a voltmeter, measure voltage between ground and MAF sensor signal circuit at connector. If reading is 5 volts, go to next step. If reading is not as specified, go to step 8).
5. Using a test light, check for voltage between sensor ground circuit and voltage supply circuit at MAF sensor harness connector. If test light comes on, go to step 13). If test light does not come on, go to next step.
6. Using a test light, check for voltage between ground and voltage supply circuit at MAF sensor connector. If test light comes on, go to step 12). If test light does not come on, go to next step.
7. Check for poor connection at MAF sensor. Repair as necessary. Retest system. If connections are okay, go to step 13).
8. Turn ignition off. Disconnect PCM harness connector related to MAF sensor circuit. Turn ignition on. Using a voltmeter, measure voltage between ground and MAF signal terminal at PCM. If reading is less than 4 volts, go to next step. If reading is not as specified, go to step 11).
9. Turn ignition off. Disconnect White PCM harness connector. Disconnect MAF sensor connector. Turn ignition on. Using a voltmeter, check MAF sensor signal circuit for short to voltage supply circuit. Repair as necessary. Retest system.
10. Turn ignition off. Disconnect White PCM harness connector. Using an ohmmeter, check sensor signal circuit between MAF sensor harness connector and PCM for an open, short to ground or short to sensor ground circuit. Repair as necessary. Retest system. If wire is okay, go to step 13).
11. Locate and repair open in sensor ground circuit between MAF sensor harness connector and PCM. Retest system.
12. Locate and repair open in voltage supply circuit between MAF sensor harness connector and PCM. Retest system.
13. Replace MAF sensor. Retest system. If DTC P0102 resets, replace PCM. Retest system.

Isuzu Trooper Limited 1997 - DTC P0103 - MASS AIRFLOW (MAF) SENSOR CIRCUIT/HIGH FREQUENCY Diagnostic Aids

An intermittent problem can be caused by misrouted harness, rubbed-through wire insulation or broken wire inside insulation. Also, check scan tool FAILURE RECORDS to determine mileage since last DTC was set.

1. Perform On-Board Diagnostic (OBD) System Check. See BASIC TESTING article. Go to next step.
2. Turn ignition on. Review and record FAILURE RECORDS data on scan tool. Operate vehicle within FAILURE RECORDS conditions. If DTC P0103 is set, go to next step. If DTC P0103 is not set, check for an intermittent problem, see DIAGNOSTIC AIDS .
3. Start engine and allow it to reach normal operating temperature. With engine at idle, monitor MAF FREQUENCY parameter on scan tool. If display is greater than 9500 Hz, go to next step. If display is 9500 Hz or less, go to step 7).
4. Turn ignition off. Disconnect MAF sensor harness connector. Start engine and let idle. Using scan tool, monitor MAF FREQUENCY parameter. If display is zero Hz, go to next step. If display is not zero Hz, go to step 6).
5. Replace MAF sensor. Retest system. If DTC P0103 resets, replace PCM. If DTC P0103 does not reset, repair is complete.
6. Check MAF sensor harness for incorrect routing near high voltage components (solenoids, relays or motors). Repair as necessary. If MAF sensor harness is okay, replace PCM. Retest system.
7. With engine at idle, monitor MAF FREQUENCY parameter on scan tool. Snap throttle wide open and release while observing scan tool display. If display reading was greater than 9500 Hz, go to step 5). If display reading was not as specified, replace PCM. Retest system.

Isuzu Trooper Limited 1997 - DTC P0106 - MANIFOLD ABSOLUTE PRESSURE (MAP) SENSOR CIRCUIT PERFORMANCE Diagnostic Aids

An intermittent problem can be caused by misrouted harness, rubbed-through wire insulation or broken wire inside insulation. Also, check scan tool FAILURE RECORDS to determine mileage since last DTC was set.

1. Perform On-Board Diagnostic (OBD) System Check. See BASIC TESTING article. Go to next step.
2. Turn ignition on. Review and record FAILURE RECORDS data on scan tool. Operate vehicle within FAILURE RECORDS conditions. If DTC P0106 is set, go to step 4). If DTC P0106 is not set, go to next step.
3. Check for the following conditions:
   • MAP sensor seal missing or damaged.
   • Vacuum hoses disconnected, damaged or misrouted.
   • Intake manifold leaks.
   • Vacuum leaks at throttle body or EGR valve and/or piping.
   • PCV valve improperly installed, damaged or missing.

   Repair as necessary. Retest system. If no problems are found, check for an intermittent problem, see DIAGNOSTIC AIDS .

4. Turn ignition off. Disconnect MAP sensor harness connector. Turn ignition on. Observe MAP sensor parameter on scan tool. If display is about 11 kPa, go to next step. If display is not as specified, go to step 13).
5. Connect a test light between battery positive terminal and sensor signal circuit at MAP sensor harness connector. If display on scan tool is about 105 kPa, go to next step. If display is not as specified, go to step 9).
6. Using a fused jumper wire, connect voltage reference circuit and signal circuit together at MAP sensor harness connector. If display on scan tool is about 104 kPa, go to next step. If display is not as specified, go to step 8).
7. Turn ignition off. Disconnect PCM harness connectors. Using an ohmmeter, check MAP sensor ground circuit for high resistance, open or poor connection. Repair as necessary. Retest system. If wire is okay, go to step 11).
8. Turn ignition off. Using an ohmmeter, check MAP sensor voltage reference circuit for high resistance, open or poor connection. Repair as necessary. Retest system. If wire is okay, go to step 10).
9. Turn ignition off. Disconnect PCM harness connectors. Using an ohmmeter, check MAP sensor signal circuit for high resistance, open or poor connection. Repair as necessary. Retest system. If wire is okay, go to next step.
10. Check MAP sensor signal circuit for poor connection at PCM. Repair as necessary. If wire is okay, replace PCM. Retest system.
11. Check for poor connection at MAP sensor. Repair as necessary. If connection is okay, replace MAP sensor. Retest system.
12. Turn ignition off. Disconnect PCM harness connectors. Turn ignition on. Using a voltmeter, check MAP sensor signal circuit for a short to battery voltage or voltage reference circuit. Repair as necessary. If wire is okay, replace PCM. Retest system.

Isuzu Trooper Limited 1997 - DTC P0107 - MANIFOLD ABSOLUTE PRESSURE (MAP) SENSOR CIRCUIT/LOW VOLTAGE Diagnostic Aids

An intermittent problem can be caused by misrouted harness, rubbed-through wire insulation or broken wire inside insulation.

If other DTC(s) are set that share same ground and/or 5-volt reference circuit, check for faulty connections or wiring. PCM's 5-volt reference circuits are internally connected within PCM. If all MAP sensor circuits are okay, check related 5-volt reference circuits. If it is determined that DTC is intermittent, check scan tool FAILURE RECORDS to determine mileage since last DTC was set.

1. Perform On-Board Diagnostic (OBD) System Check. See BASIC TESTING article. Go to next step.
2. Turn ignition on. With throttle fully closed, observe MAP sensor parameter on scan tool. If display is 11 kPa at sea level, go to step 4). If display is not as specified, go to next step.
3. Turn ignition on. Review and record FAILURE RECORDS data on scan tool. Operate vehicle within FAILURE RECORDS conditions. If DTC P0107 is set, go to next step. If DTC P0107 is not set, check for an intermittent problem, see DIAGNOSTIC AIDS .
4. Turn ignition off. Disconnect MAP sensor harness connector. Using a fused jumper wire, connect sensor voltage reference circuit and sensor signal circuit together at MAP sensor harness connector. Turn ignition on. Observe MAP sensor parameter on scan tool. If display is about 5 volts and 104 kPa, replace MAP sensor. Retest system. If display is not as specified, go to next step.
5. Remove jumper wire. Connect a test light between battery positive terminal and sensor signal circuit at MAP sensor harness connector. If display on scan tool is about 5 volts and 104 kPa, go to next step. If display is not as specified, go to step 8).
6. Turn ignition off. Disconnect PCM harness connectors. Using an ohmmeter, check voltage reference circuit for an open or short to ground. Repair as necessary. Retest system. If wire is okay, go to next step.
7. Check voltage reference circuit for poor connection at PCM. Repair as necessary. If connection is okay, replace PCM. Retest system.
8. Turn ignition off. Disconnect PCM harness connectors. Using an ohmmeter, check MAP sensor signal circuit for an open, short to ground or short to sensor ground circuit. Repair as necessary. Retest system. If wire is okay, go to next step.
9. Check MAP sensor signal circuit for a poor connection at PCM or MAP sensor. Repair as necessary. If wire is okay, replace PCM. Retest system.

Isuzu Trooper Limited 1997 - DTC P0108 - MANIFOLD ABSOLUTE PRESSURE (MAP) SENSOR CIRCUIT/HIGH VOLTAGE Diagnostic Aids

An intermittent problem can be caused by misrouted harness, rubbed-through wire insulation or broken wire inside insulation. If it is determined that DTC is intermittent, performing DTC P1108 diagnostics may isolate cause of fault.

1. Perform On-Board Diagnostic (OBD) System Check. See BASIC TESTING article. Go to next step.

   NOTE:

   If idle is rough or unstable, repair idle problem first. See TESTS W/O CODES article.

2. Start engine and allow it to reach normal operating temperature. With engine at idle, note MAP sensor value on scan tool. If display is greater than 90 kPa, go to step 4). If reading is not as specified, go to next step.
3. Turn ignition on. Review and record FAILURE RECORDS data on scan tool. Operate vehicle within FAILURE RECORDS conditions. If DTC P0108 is set, go to next step. If DTC P0108 is not set, check for an intermittent problem, see DIAGNOSTIC AIDS .
4. Turn ignition off. Disconnect MAP sensor harness connector. Turn ignition on. Note MAP sensor voltage on scan tool. If display is zero volts and 11 kPa, go to next step. If display is not as specified, go to step 6).
5. Using a test light connected to ground, probe MAP sensor ground circuit. If test light comes on, go to step 7). If test light does not come on, go to step 9).
6. Using a voltmeter, check MAP sensor signal circuit for a short to battery voltage or voltage reference circuit. Repair as necessary. If wire is okay, replace PCM. Retest system.
7. Check for poor ground circuit connection at MAP sensor harness connector. Repair as necessary. Retest system. If connection is okay, go to next step.
8. Check for restricted or leaking vacuum hose to MAP sensor. Repair as necessary. If vacuum supply is okay, replace MAP sensor. Retest system.
9. Check for poor MAP sensor ground circuit connection at PCM. Repair as necessary. Retest system. If connection is okay, go to next step.
10. Turn ignition off. Using an ohmmeter, measure resistance between MAP sensor ground circuit at MAP sensor harness connector and chassis ground. If resistance is greater than 5 ohms, repair open or poor connection. If MAP sensor ground is okay, replace PCM. Retest system.

Isuzu Trooper Limited 1997 - DTC P0112 - INTAKE AIR TEMPERATURE (IAT) CIRCUIT/LOW VOLTAGE Diagnostic Aids

An intermittent problem can be caused by misrouted harness, rubbed-through wire insulation or broken wire inside insulation. If it is determined that DTC is intermittent, check scan tool FAILURE RECORDS to determine mileage since last DTC was set.

1. Perform On-Board Diagnostic (OBD) System Check. See BASIC TESTING article. Go to next step.
2. Turn ignition on. Using scan tool, monitor IAT sensor parameter. If display is greater than 283?F (148?C), go to step 4). If display is not as specified, go to next step.
3. Turn ignition on. Review and record FAILURE RECORDS data on scan tool. Operate vehicle within FAILURE RECORDS conditions. If DTC P0112 is set, check resistance of IAT sensor at specified temperatures. See INTAKE AIR TEMPERATURE (IAT) SENSOR RESISTANCE . Replace IAT sensor if it does not test as specified. If DTC P0112 is not set, check for an intermittent problem, see DIAGNOSTIC AIDS .
   

   Isuzu Trooper Limited 1997 INTAKE AIR TEMPERATURE (IAT) SENSOR RESISTANCE
   

   Temperature ?F (?C)	Ohms
   -40 (-40)	100,700
   -22 (-30)	52,700
   5 (-15)	21,450
   23 (-5)	12,300
   41 (5)	7280
   59 (15)	4450
   77 (25)	2796
   95 (35)	1802
   113 (45)	1188
   140 (60)	667
   176 (80)	332
   212 (100)	177

4. Turn ignition off. Disconnect IAT sensor harness connector. Turn ignition on. Observe IAT parameter on scan tool. If display is less than -36?F, replace IAT sensor. Retest system. If display is not as specified, go to next step.
5. Turn ignition off. Disconnect PCM harness connectors. Using an ohmmeter, check IAT sensor signal circuit for short to ground. Repair as necessary. If wire is okay, replace PCM. Retest system.

Isuzu Trooper Limited 1997 - DTC P0113 - INTAKE AIR TEMPERATURE (IAT) CIRCUIT/HIGH VOLTAGE Diagnostic Aids

An intermittent problem can be caused by misrouted harness, rubbed-through wire insulation or broken wire inside insulation.

If other DTC(s) are set that share same ground and/or 5-volt reference circuit, check for faulty connections or wiring. PCM 5-volt reference circuits are internally connected within PCM.

If it is determined that DTC is intermittent, check scan tool FAILURE RECORDS to determine mileage since last DTC was set.

1. Perform On-Board Diagnostic (OBD) System Check. See BASIC TESTING article. Go to next step.
2. Turn ignition on. Using scan tool, monitor IAT sensor parameter. If display is less than -36?F (-38?C), go to step 4). If display is not as specified, go to next step.
3. Turn ignition on. Review and record FAILURE RECORDS data on scan tool. Operate vehicle within FAILURE RECORDS conditions. If DTC P0113 is set, check resistance of IAT sensor at specified temperatures. See INTAKE AIR TEMPERATURE (IAT) SENSOR RESISTANCE in DTC P0112. Replace IAT sensor if it does not test as specified. If DTC P0113 is not set, check for an intermittent problem, see DIAGNOSTIC AIDS .
4. Turn ignition off. Disconnect IAT sensor harness connector. Using a fused jumper wire, connect terminals of IAT sensor harness connector together. Turn ignition on. Observe IAT sensor parameter on scan tool. If display is 284?F (140?C), go to step 6). If display is not as specified, go to next step.
5. Jumper IAT sensor signal circuit to ground. If display on scan tool is 284?F (140?C), go to step 7). If display is not 284?F (140?C), go to step 8).
6. Check for poor connections at IAT sensor harness connector. Repair as necessary. If connections are okay, replace IAT sensor. Retest system.
7. Turn ignition off. Disconnect PCM harness connectors. Using an ohmmeter, check IAT sensor ground circuit for an open. Repair as necessary. Retest system. If wire is okay, go to step 9).
8. Turn ignition off. Disconnect PCM harness connector. Using an ohmmeter, check IAT sensor signal circuit for an open. Repair as necessary. Retest system. If wire is okay, go to next step.
9. Check for a poor IAT sensor ground circuit or signal circuit connection at PCM. Repair as necessary. If wires are okay, replace PCM. Retest system.

Isuzu Trooper Limited 1997 - DTC P0117 - ENGINE COOLANT TEMPERATURE (ECT) CIRCUIT/LOW VOLTAGE Diagnostic Aids

An intermittent problem can be caused by misrouted harness, rubbed-through wire insulation or broken wire inside insulation.

If DTC cannot be duplicated, check scan tool FAILURE RECORDS to determine mileage since last DTC was set. If it is determined that DTC is intermittent, performing DTC P1114 diagnostics may isolate cause of fault.

1. Perform On-Board Diagnostic (OBD) System Check. See BASIC TESTING article. Go to next step.
2. Turn ignition on. Using scan tool, select ENG COOL TEMP. If display is less than 282?F (139?C), go to step 4). If display is not as specified, go to next step.
3. Turn ignition on. Review and record FAILURE RECORDS data on scan tool. Operate vehicle within FAILURE RECORDS conditions. If DTC P0117 is set, check resistance of ECT sensor at specified temperatures. See ENGINE COOLANT TEMPERATURE (ECT) SENSOR RESISTANCE . Replace ECT sensor if it does not test as specified. If DTC P0117 is not set, check for an intermittent problem. See TESTS W/O CODES article.
   

   Isuzu Trooper Limited 1997 ENGINE COOLANT TEMPERATURE (ECT) SENSOR RESISTANCE
   

   Temperature ?F (?C)	Ohms
   -40 (-40)	100,700
   -22 (-30)	52,700
   5 (-15)	21,450
   23 (-5)	12,300
   41 (5)	7280
   59 (15)	4450
   77 (25)	2796
   95 (35)	1802
   113 (45)	1188
   140 (60)	667
   176 (80)	332
   212 (100)	177

4. Turn ignition off. Disconnect ECT sensor harness connector. Turn ignition on. Observe ENG COOL TEMP on scan tool. If display is -38?F (-38?C), replace ECT sensor. Retest system. If display is not as specified, go to next step.
5. Turn ignition off. Disconnect PCM harness connectors. Using an ohmmeter, check ECT sensor signal circuit for short to sensor ground circuit. Repair as necessary. If wire is okay, replace PCM. Retest system.

Isuzu Trooper Limited 1997 - DTC P0118 - ENGINE COOLANT TEMPERATURE (ECT) CIRCUIT/HIGH VOLTAGE Diagnostic Aids

An intermittent problem can be caused by misrouted harness, rubbed-through wire insulation or broken wire inside insulation.

If DTC cannot be duplicated, check scan tool FAILURE RECORDS to determine mileage since last DTC was set. If it is determined that DTC is intermittent, performing DTC P1115 diagnostics may isolate cause of fault.

1. Perform On-Board Diagnostic (OBD) System Check. See BASIC TESTING article. Go to next step.
2. Turn ignition on. Using scan tool, select ENG COOL TEMP. If display is less than -38?F (-39?C), go to step 4). If display is not as specified, go to next step.
3. Turn ignition on. Review and record FAILURE RECORDS data on scan tool. Operate vehicle within FAILURE RECORDS conditions. If DTC P0118 is set, check resistance of ECT sensor at specified temperatures. See ENGINE COOLANT TEMPERATURE (ECT) SENSOR RESISTANCE table in DTC P0117. Replace ECT sensor if it does not test as specified. If DTC P0118 is not set, check for an intermittent problem, see DIAGNOSTIC AIDS . See TESTS W/O CODES article.
4. Turn ignition off. Disconnect ECT sensor harness connector. Using a fused jumper wire, connect terminals of ECT sensor harness connector together. Turn ignition on. Observe ENG COOL TEMP value on scan tool. If display is 284?F (140?C), go to step 6). If display is not as specified, go to next step.
5. Jumper ECT sensor signal circuit to ground. If display on scan tool is 284?F ()140?C, go to step 7). If display is not as specified, go to step 8).
6. Check for poor connections at ECT sensor harness connector. Repair as necessary. If connections are okay, replace ECT sensor. Retest system.
7. Turn ignition off. Disconnect PCM harness connectors. Using an ohmmeter, check ECT sensor ground circuit for an open. Repair as necessary. Retest system. If wire is okay, go to step 9).
8. Turn ignition off. Disconnect PCM harness connector. Using an ohmmeter, check ECT sensor signal circuit for an open. Repair as necessary. Retest system. If wire is okay, go to next step.
9. Check for a poor ECT sensor ground circuit or signal circuit connection at PCM. Repair as necessary. If wires are okay, replace PCM. Retest system.

Isuzu Trooper Limited 1997 - DTC P0121 - THROTTLE POSITION (TP) SENSOR CIRCUIT PERFORMANCE Diagnostic Aids

An intermittent problem can be caused by misrouted harness, rubbed-through wire insulation or broken wire inside insulation.

Low MAP reading can cause PCM incorrect of TP sensor value by PCM. If DTC cannot be duplicated, check scan tool FAILURE RECORDS to determine mileage since last DTC was set. If it is determined that DTC is intermittent, performing DTCs P1121 and DTC P1122 diagnostics may isolate cause of fault.

1. Perform On-Board Diagnostic (OBD) System Check. See BASIC TESTING article. Go to next step.
2. Turn ignition on. Observe MAP sensor parameter on scan tool. If display is less than 65 kPa, go to next step. If display is not as specified, go to step 5).
3. Turn ignition off. Disconnect MAP sensor harness connector. Connect a test light between MAP sensor voltage reference circuit and MAP sensor signal circuit at harness connector. Turn ignition on. If display on scan tool is less than 65 kPa, replace MAP sensor. Retest system. If display is not as specified, go to next step.
4. Turn ignition off. Using an ohmmeter, check for an open, short to ground or short to MAP sensor ground circuit. Repair as necessary. If wire is okay, replace PCM. Retest system.
5. Observe TP sensor angle on scan tool while slowly opening throttle. If display shows a steady increase from zero percent to 100 percent, check for an intermittent problem, see DIAGNOSTIC AIDS . If display is not as specified, go to next step.
6. Turn ignition off. Disconnect TP sensor harness connector. Turn ignition on. Observe TP sensor parameter on scan tool. If display is zero volts, go to next step. If display is not as specified, go to step 8).
7. Turn ignition off. Connect a test light between voltage reference circuit and sensor signal circuit at TP sensor harness connector. Turn ignition on. If display is 5 volts, replace TP sensor. Retest system. If display is not as specified, go to step 9).
8. Check for the following items:
   • TP sensor signal circuit shorted to power.
   • High resistance in TP sensor ground circuit. Repair as necessary. If no problems are found, replace PCM. Retest system.
9. Check for the following items:
   • Poor connection in TP sensor signal circuit or voltage reference circuit.
   • High resistance in TP sensor voltage reference circuit. Repair as necessary. If no problems are found, replace PCM. Retest system.

Isuzu Trooper Limited 1997 - DTC P0122 - THROTTLE POSITION (TP) SENSOR CIRCUIT/LOW VOLTAGE Diagnostic Aids

An intermittent problem can be caused by misrouted harness, rubbed-through wire insulation or broken wire inside insulation.

If other DTC(s) are set that share same ground and/or 5-volt reference circuit, check for faulty connections or wiring. The PCM 5-volt reference circuits are internally connected within PCM.

If DTC cannot be duplicated, check scan tool FAILURE RECORDS to determine mileage since last DTC was set. If it is determined that DTC is intermittent, performing DTC P1122 diagnostics may isolate cause of fault.

1. Perform On-Board Diagnostic (OBD) System Check. See BASIC TESTING article. Go to next step.
2. Turn ignition on. With throttle closed, observe TP sensor parameter on scan tool. If display is less than 0.22 volt, go to step 4). If display is not as specified, go to next step.
3. Turn ignition on. Review and record FAILURE RECORDS data on scan tool. Operate vehicle within FAILURE RECORDS conditions. If DTC P0122 is set, go to next step. If DTC P0122 is not set, check for an intermittent problem, see DIAGNOSTIC AIDS .
4. Turn ignition off. Disconnect TP sensor harness connector. Using a fused jumper wire, connect voltage reference circuit to sensor signal circuit at harness connector. Turn ignition on. Observe display on scan tool. If display is 5 volts, go to step 10). If display is not as specified, go to next step.
5. Remove jumper wire. Connect a test light between battery positive terminal and sensor signal circuit at TP sensor harness connector. If display on scan tool is 5 volts, go to next step. If display is not as specified, go to step 8).
6. Turn ignition off. Disconnect PCM harness connector. Using an ohmmeter, check for an open or short to ground in voltage reference circuit. Repair as necessary. Retest system. If wire is okay, go to next step.
7. Check voltage reference circuit for poor connection at PCM. Repair as necessary. If connection is okay, replace PCM. Retest system.
8. Turn ignition off. Disconnect PCM harness connector. Using an ohmmeter, check TP sensor signal circuit for an open, short to ground or short to sensor ground circuit. Repair as necessary. Retest system. If wire is okay, go to next step.
9. Check TP sensor signal circuit for poor connection at PCM. Repair as necessary. If connection is okay, replace PCM. Retest system.
10. Check TP sensor signal circuit for poor connection at TP sensor. Repair as necessary. If connection is okay, replace TP sensor. Retest system.

Isuzu Trooper Limited 1997 - DTC P0123 - THROTTLE POSITION (TP) SENSOR CIRCUIT/LOW VOLTAGE Diagnostic Aids

An intermittent problem can be caused by misrouted harness, rubbed-through wire insulation or broken wire inside insulation.

If other DTC(s) are set that share same ground and/or 5-volt reference circuit, check for faulty connections or wiring. The PCM 5-volt reference circuits are internally connected within PCM.

If DTC cannot be duplicated, check scan tool FAILURE RECORDS to determine mileage since last DTC was set. If it is determined that DTC is intermittent, performing DTC P1121 diagnostics may isolate cause of fault.

1. Perform On-Board Diagnostic (OBD) System Check. See BASIC TESTING article. Go to next step.
2. Turn ignition on. With throttle closed, observe TP sensor parameter on scan tool. If display is greater than 4.88 volts, go to step 4). If display is not as specified, go to next step.
3. Turn ignition on. Review and record FAILURE RECORDS data on scan tool. Operate vehicle within FAILURE RECORDS conditions. If DTC P0123 is set, go to next step. If DTC P0123 is not set, check for an intermittent problem, see DIAGNOSTIC AIDS .
4. Turn ignition off. Disconnect TP sensor harness connector. Turn ignition on. Observe display on scan tool. If display is about zero volts, go to next step. If display is not as specified, go to step 6).
5. Using a test light connected to battery positive terminal, probe TP sensor ground circuit at harness connector. If test light comes on, go to step 7). If test light does not come on, go to step 10).
6. Turn ignition off. Disconnect PCM harness connector. Turn ignition on. Using a voltmeter, check TP sensor signal circuit for a short to power. Repair as necessary. If wire is okay, replace PCM. Retest system.
7. Turn ignition on. Observe TP sensor parameter on scan tool while disconnecting each sensor which shares same voltage reference circuit. See WIRING DIAGRAMS article. If display changes while disconnecting a sensor, replace that sensor. Repair as necessary. If display does not change, go to next step.
8. Turn ignition off. Disconnect PCM harness connectors. Turn ignition on. Using a voltmeter, check voltage reference circuit for short to battery voltage. Repair as necessary. Retest system. If wire is okay, go to next step.
9. Check for poor connection at TP sensor. Repair as necessary. If connection is okay, replace TP sensor. Retest system.
10. Turn ignition off. Disconnect PCM harness connectors. Using an ohmmeter, check for open in TP sensor ground circuit. Repair as necessary. If wire is okay, replace PCM. Retest system.

Isuzu Trooper Limited 1997 - DTC P0125 - INSUFFICIENT COOLANT TEMPERATURE FOR CLOSED LOOP Diagnostic Aids

An intermittent problem can be caused by misrouted harness, rubbed-through wire insulation or broken wire inside insulation. If DTC cannot be duplicated, check scan tool FAILURE RECORDS to determine mileage since last DTC was set.

1. Perform On-Board Diagnostic (OBD) System Check. See BASIC TESTING article. Go to next step.
2. If any Engine Coolant Temperature (ECT) DTCs are set, see appropriate DTC test. If no DTCs are set, go to next step.
3. Allow engine to cool. Ensure coolant level is full. If coolant level is okay, go to next step. If coolant level is low, check cooling system for leaks. Repair as necessary. Retest system.
4. Start engine and let idle. Using scan tool select ENG COOL TEMP. If display increases to greater than 70?F (21?C) within 2 minutes, check for an intermittent problem, see DIAGNOSTIC AIDS . If display is not as specified, go to next step.
5. Check thermostat for proper operation. Replace thermostat if necessary. Retest system. If thermostat is okay, go to next step.
6. Using a thermometer, check temperature of water in radiator. Compare reading with display on scan tool. If readings are fairly close, check for sticking thermostat or incorrect thermostat application. Repair as necessary. If display readings are not close, go to next step.
7. Turn ignition off. Disconnect PCM harness connectors. Using an ohmmeter, measure resistance between ECT sensor signal circuit and ECT sensor ground circuit at PCM harness connector. Compare resistance reading with coolant temperature. See ENGINE COOLANT TEMPERATURE RESISTANCE . If readings are as specified, replace PCM. Retest system. If readings are not as specified, go to next step.
   

   Isuzu Trooper Limited 1997 ENGINE COOLANT TEMPERATURE (ECT) SENSOR RESISTANCE
   

   Temperature ?F (?C)	Ohms
   -40 (-40)	100,700
   -22 (-30)	52,700
   5 (-15)	21,450
   23 (-5)	12,300
   41 (5)	7280
   59 (15)	4450
   77 (25)	2796
   95 (35)	1802
   113 (45)	1188
   140 (60)	667
   176 (80)	332
   212 (100)	177

8. Using an ohmmeter, check for high resistance in ECT sensor signal circuit or sensor ground circuit. Check for poor connections at PCM and ECT sensor. Repair as necessary. If ECT sensor circuit is okay, replace ECT sensor. Retest system.

Isuzu Trooper Limited 1997 - DTC P0131 - HEATED OXYGEN SENSOR (HO2S) NO. 1 BANK 1/LOW VOLTAGE

NOTE:

ALWAYS inspect a faulty HO2S for contamination and correct cause before installing a new HO2S.

Isuzu Trooper Limited 1997 - Diagnostic Aids

Check for HO2S pigtail wire for breaks, contamination or grounding on exhaust manifold. Check for intermittent ground in signal wire between sensor connector and sensor.

Check for lean injector(s). Perform Injector Balance Test. See SYSTEM/COMPONENT TESTS article. Check for fuel contamination, improper fuel pressure or exhaust leak, especially near HO2S. Check for vacuum or crankcase leak, causing a lean condition.

1. Perform On-Board Diagnostic (OBD) System Check. See BASIC TESTING article. Go to next step.
2. Start engine and allow it to reach normal operating temperature. Using scan tool, observe HO2S No. 1, bank 1 parameter on scan tool. If display remains less than 22 mV, go to step 4). If display is not as specified, go to next step.
3. Turn ignition on. Review and record FAILURE RECORDS data on scan tool. Operate vehicle within FAILURE RECORDS conditions. If DTC P0131 is set, go to next step. If DTC P0131 is not set, check for an intermittent problem, see DIAGNOSTIC AIDS .
4. Turn ignition off. Disconnect PCM harness connectors. Using an ohmmeter, check HO2S No. 1, bank 1 high and low circuits for a short to ground or short to heater ground circuit. Repair as necessary. Retest system. If wires are okay, go to next step.
5. Disconnect HO2S No. 1, bank 1 harness connector. Using an ohmmeter, check for continuity between high and low signal circuits at harness connector. If continuity is present, check for short between wires and repair as necessary. Retest system. If continuity is not present, go to next step.
6. Reconnect PCM, leaving sensor disconnected. Turn ignition on. If HO2S No. 1, bank 1 parameter on scan tool is 425-475 mV, check for an intermittent problem, see DIAGNOSTIC AIDS . If reading is not as specified, replace PCM. Retest system.

Isuzu Trooper Limited 1997 - DTC P0132 - HEATED OXYGEN SENSOR (HO2S) NO. 1 BANK 1/HIGH VOLTAGE

NOTE:

ALWAYS inspect a faulty HO2S for contamination and correct cause before installing a new HO2S.

Isuzu Trooper Limited 1997 - Diagnostic Aids

Check fuel pressure. Perform INJECTOR BALANCE TEST. See FUEL SYSTEM in appropriate SYSTEM/COMPONENT TESTS article. Check for leaking fuel pressure regulator by removing vacuum hose and checking for fuel presence. If fuel is present, replace regulator. Check EVAP canister for fuel saturation. Check MAF sensor. Check TP sensor. See SYSTEM/COMPONENT TESTS article.

1. Perform On-Board Diagnostic (OBD) System Check. See BASIC TESTING article. Go to next step.
2. Start engine and allow it to reach normal operating temperature. Using scan tool, observe HO2S No. 1, bank 1 parameter. If display remains greater than 952 mV, go to step 4). If display is not as specified, go to next step.
3. Turn ignition on. Review and record FAILURE RECORDS data on scan tool. Operate vehicle within FAILURE RECORDS conditions. If DTC P0132 is set, go to next step. If DTC P0132 is not set, check for an intermittent problem, see DIAGNOSTIC AIDS .
4. Turn ignition off. Disconnect HO2S No. 1, bank 1. Turn ignition on. Using a voltmeter, measure voltage of high and low signal circuits at harness connector (PCM side). If reading is 3-4 volts at either wire, repair signal circuit for short to power. If reading is not as specified, go to next step.
5. Turn ignition on. Jumper high and low signal circuits of connector (PCM side) to ground. If display on scan tool is less than 10 mV, go to next step. If reading is not as specified, replace PCM. Retest system.
6. Disconnect jumper from signal circuits. Using scan tool, observe replace HO2S No. 1, bank 1 parameter. If display remains is 425-475 mV, see DIAGNOSTIC AIDS . If display remains is not 425-475 mV, replace PCM. Retest system.

Isuzu Trooper Limited 1997 - DTC P0133 - HEATED OXYGEN SENSOR (HO2S) NO. 1 BANK 1/SLOW RESPONSE

NOTE:

ALWAYS inspect a faulty HO2S for contamination and correct cause before installing a new HO2S.

NOTE:

If any DTCs are set (except for P0153, P1133, P1134, P1153 and/or P1154), diagnose them first.

Isuzu Trooper Limited 1997 - Diagnostic Aids

An intermittent problem can be caused by misrouted harness, rubbed-through wire insulation or broken wire inside insulation. If DTC cannot be duplicated, check scan tool FAILURE RECORDS to determine mileage since last DTC was set.

1. Perform On-Board Diagnostic (OBD) System Check. See BASIC TESTING article. Go to next step.
2. Start engine and allow it to reach operating temperature. Operate vehicle within conditions required to set DTC:
   • Engine in closed loop.
   • Engine running for one minute or more.
   • Engine RPM is 1500-3000.
   • Canister purge duty cycle is 2 percent or more.
   • MAF is 9-42 grams per second.
   • All conditions for 3 seconds or more.
   • Rich-to-lean transition is longer than 105 milliseconds.
   • Lean-to-Rich transition is longer than 94 milliseconds.

   Using scan tool, observe SPECIFIC DTC parameter. If scan tool displays DTC P0133 FAILED THIS IGN, go to next step. If scan tool does not display DTC P0133 FAILED THIS IGN, check for an intermittent problem, see DIAGNOSTIC AIDS .

3. If scan tool also displays DTC P0153, P1133, P1134, P1153 and/or P1154 FAILED THIS IGN, replace affected HO2S. Retest system. If scan tool does not display these DTCs, go to next step.
4. Visually inspect exhaust system for leaks near HO2S No. 1, bank 1. If leaks are found, repair as necessary and return to step 2). If no leaks are found, go to next step.
5. Visually inspect HO2S No. 1, bank 1 for proper installation. Check for corrosion on terminals. Check terminal tension at HO2S No. 1, bank 1 and PCM. Repair as necessary. If no problem is found, go to next step.
6. Disconnect HO2S No. 1, bank 1 harness connector. Using a voltmeter, measure voltage between high signal circuit and ground, then low signal circuit and ground. If reading is 3-4 volts, go to next step. If reading is not as specified, go to step 8).
7. Using a fused jumper wire, connect high and low signal circuits of HO2S No. 1, bank 1 harness connector (PCM side) to ground. Turn ignition on. Using scan tool, monitor voltage. If reading is less than 10 mV and immediately returns to about 450 mV when jumper wire is removed, replace HO2S No. 1, bank 1. If reading is not as specified, replace PCM. Retest system.
8. Inspect PCM connections and terminals for damage. Repair as necessary. Retest system. If PCM connections and terminals are okay, go to next step.
9. Repair open, short or grounded HO2S No. 1, bank 1 high or low signal circuits. Retest system.

Isuzu Trooper Limited 1997 - DTC P0134 - HEATED OXYGEN SENSOR (HO2S) NO. 1 BANK 1/INSUFFICIENT ACTIVITY

NOTE:

ALWAYS inspect a faulty HO2S for contamination and correct cause before installing a new HO2S.

Isuzu Trooper Limited 1997 - Diagnostic Aids

An intermittent may be caused by a poor connection, rubbed through wire insulation or a broken wire inside insulation. Inspect harness connectors for backed out terminals, improper mating, broken locks, improperly formed or damaged terminals, poor terminal-to-wire connection, and damaged harness.

Using scan tool, monitor signal voltage while wiggling HO2S related connectors and wiring harness with a warm engine running at part throttle in closed loop. If a failure is induced, signal voltage will change from normal fluctuating voltage to a fixed voltage. A change in voltage will assist in isolating location of fault. DO NOT solder HO2S wires.

1. Perform On-Board Diagnostic (OBD) System Check. See BASIC TESTING article. Go to next step.
2. Start engine and allow it to reach normal operating temperature. Apply parking brake and increase engine speed to greater than 1200 RPM for 2 minutes. Using scan tool, observe HO2S No. 1, bank 1 parameter. If reading varies outside 400-500 mV range, turn engine off and go to next step. If reading does not vary outside 400-500 mV range, go to step 4).
3. Turn ignition on. Review and record FAILURE RECORDS data on scan tool. Operate vehicle within FAILURE RECORDS conditions. If DTC P0134 is set, go to next step. If DTC P0134 is not set, check for an intermittent problem, see DIAGNOSTIC AIDS .
4. Inspect sensor harness for damage. Repair as necessary. If harness is okay, go to next step.
5. Check for poor signal circuit connections at HO2S No. 1, bank 1 harness connector. Repair as necessary. Retest system. If connection is okay, go to next step.
6. Check for poor HO2S No. 1, bank 1 signal circuit connections at PCM harness connectors. Repair as necessary. Retest system. If connections are okay, go to next step.
7. Turn ignition off. Disconnect PCM connectors. Using an ohmmeter, measure resistance of HO2S No. 1, bank 1 high signal circuit between PCM and HO2S. If resistance is greater than 5 ohms, repair open or poor connection. Retest system. If wire is okay, go to next step.
8. Measure resistance of HO2S No. 1, bank 1 low signal circuit between PCM and HO2S. If resistance is greater than 5 ohms, repair open or poor connection. Retest system. If wire is okay, reconnect PCM connectors and go to next step.
9. Disconnect HO2S No. 1, bank 1 connector. Turn ignition on. Using a fused jumper wire, connect high and low signal circuits of HO2S No. 1, bank 1 (PCM side) to ground. If scan tool display is 0-10 mV, replace HO2S No. 1, bank 1. If display is not as specified, replace PCM. Retest system.

Isuzu Trooper Limited 1997 - DTC P0135 - HEATED OXYGEN SENSOR (HO2S) NO. 1 BANK 1/HEATER CIRCUIT

NOTE:

ALWAYS inspect a faulty HO2S for contamination and correct cause before installing a new HO2S.

Isuzu Trooper Limited 1997 - Diagnostic Aids

An intermittent may be caused by a poor connection, rubbed through wire insulation or a broken wire inside insulation. Inspect harness connectors for backed out terminals, improper mating, broken locks, improperly formed or damaged terminals, poor terminal-to-wire connection, and damaged harness. If DTC cannot be duplicated, check scan tool FAILURE RECORDS to determine mileage since last DTC was set.

1. Perform On-Board Diagnostic (OBD) System Check. See BASIC TESTING article. Go to next step.
2. Allow engine to cool. Disconnect fuel pump relay. Connect fused jumper between fuel pump relay socket positive battery terminal and relay wire that goes to fuel pump and HO2S. Turn ignition off. Install scan tool. Turn ignition on. Observe HO2S No. 1, bank 1 parameter on scan tool for several minutes. If display is greater than 650 mV or less than 250 mV, check for an intermittent problem, see DIAGNOSTIC AIDS . If display is not as specified, go to next step.
3. Inspect HO2S heater fuse (20-amp) in engine compartment fuse box. If fuse is blown, check for short in circuit and replace fuse. Retest system. If fuse is okay, go to next step.
4. Turn ignition off. Raise and support vehicle. Disconnect HO2S No. 1, bank 1 harness connector. Turn ignition on. Using a test light connected to ground, probe ignition feed circuit at connector (PCM side). If test light comes on, go to next step. If test light does not come on, go to step 7).
5. Connect test light between ignition feed circuit and ground circuit at connector (PCM side). If test light comes on, go to next step. If test light does not come on, go to step 8).
6. Turn ignition off. Ensure HO2S No. 1 is cool. Using an ohmmeter, measure resistance between ignition feed circuit and heater ground circuit at HO2S No. 1 harness connector (sensor side). If resistance is 3-6 ohms, go to step 9). If resistance is not as specified, go to step 10).
7. Repair open in HO2S No. 1 ignition feed circuit. Retest system.
8. Repair open in HO2S No. 1 ground circuit. Retest system.
9. Check for poor connection at HO2S No. 1, bank 1 harness terminals. Repair as necessary. Retest system. If harness is okay, go to next step.
10. Check for poor connection at HO2S No. 1, bank 1 high or low circuit terminal connections at harness connector. Repair as necessary. Retest system. If connections are okay, go to next step.
11. Turn ignition off. Disconnect PCM harness connector terminals. Using an ohmmeter, measure resistance of HO2S No. 1, bank 1 high and low signal circuits at PCM harness connector. If either circuit resistance is greater than 5 ohms, check for an open or poor connection. Repair as necessary. If wires are okay, go to next step.
12. Check for poor HO2S No. 1, bank 1 terminal connections at PCM. Repair as necessary. If connections are okay, replace HO2S No. 1, bank 1. Retest system.

Isuzu Trooper Limited 1997 - DTC P0137 - HEATED OXYGEN SENSOR (HO2S) NO. 2 BANK 1/LOW VOLTAGE

NOTE:

ALWAYS inspect a faulty HO2S for contamination and correct cause before installing a new HO2S.

Isuzu Trooper Limited 1997 - Diagnostic Aids

Check for sensor pigtail contacting exhaust system. Ensure PCM grounds are okay. Check fuel pressure. Perform INJECTOR BALANCE TEST. See FUEL SYSTEM in appropriate SYSTEM/COMPONENT TESTS article. Check vacuum hoses for leaks at intake, throttle body, PCV and EGR systems. Inspect exhaust system for leaks. MAF sensor can go lean, disconnect MAF and recheck.

1. Perform On-Board Diagnostic (OBD) System Check. See BASIC TESTING article. Go to next step.
2. Start engine and allow it to reach normal operating temperature. Observe HO2S No. 2, bank 1 parameter on scan tool. If display remains less than 22 mV, go to step 4). If display is not as specified, go to next step.
3. Turn ignition on. Review and record FAILURE RECORDS data on scan tool. Operate vehicle within FAILURE RECORDS conditions. If DTC P0137 is set, go to next step. If DTC P0137 is not set, check for an intermittent problem, see DIAGNOSTIC AIDS .
4. Turn ignition off. Disconnect PCM harness connectors. Using an ohmmeter, check HO2S No. 2, bank 1 high and low signal circuits for a short to ground or short to heater ground circuit. Repair as necessary. Retest system. If wires are okay, go to next step.
5. Disconnect HO2S No. 2, bank 1 harness connector. Using an ohmmeter, check for continuity between high and low signal circuits at harness connector. If continuity is present, check for short between wires and repair as necessary. Retest system. If continuity is not present, go to next step.
6. Reconnect PCM, leaving sensor disconnected. Turn ignition on. If HO2S No. 2, bank 1 parameter on scan tool is 425-475 mV, check for an intermittent problem, see DIAGNOSTIC AIDS . If reading is not as specified, replace PCM. Retest system.

Isuzu Trooper Limited 1997 - DTC P0138 - HEATED OXYGEN SENSOR (HO2S) NO. 2 BANK 1/HIGH VOLTAGE

NOTE:

ALWAYS inspect a faulty HO2S for contamination and correct cause before installing a new HO2S.

Isuzu Trooper Limited 1997 - Diagnostic Aids

Check fuel pressure. Perform INJECTOR BALANCE TEST. See FUEL SYSTEM in appropriate SYSTEM/COMPONENT TESTS article. Check for leaking fuel pressure regulator by removing vacuum hose and checking for fuel presence. If fuel is present, replace regulator.

Check EVAP canister for fuel saturation. Check TP sensor. See SYSTEM/COMPONENT TESTS article. MAF sensor can go rich, disconnect MAF and recheck.

1. Perform On-Board Diagnostic (OBD) System Check. See BASIC TESTING article. Go to next step.
2. Start engine and allow it to reach normal operating temperature. Observe HO2S No. 2, bank 1 parameter on scan tool. If display remains greater than 952 mV, go to step 4). If display is not as specified, go to next step.
3. Turn ignition on. Review and record FAILURE RECORDS data on scan tool. Operate vehicle within FAILURE RECORDS conditions. If DTC P0138 is set, go to next step. If DTC P0138 is not set, check for an intermittent problem, see DIAGNOSTIC AIDS .
4. Turn ignition off. Disconnect HO2S No. 2, bank 1. Turn ignition on. Using a voltmeter, measure voltage of high and low signal circuits at harness connector (PCM side). If reading is 3-4 volts at either wire, repair signal circuit for short to power. If reading is not as specified, go to next step.
5. Turn ignition on. With HO2S No. 2, bank 1 disconnected, jumper high and low signal circuits at connector (PCM side) to ground. If display on scan tool is less than 10 mV, go to next step. If reading is not as specified, replace PCM. Retest system.
6. Disconnect jumpers. With HO2S connector disconnected, observe HO2S No. 2, bank 1 parameter on scan tool. If voltage is, 425-475 mV, check for an intermittent problem, see DIAGNOSTIC AIDS . If reading is not as specified, replace PCM. Retest system.

Isuzu Trooper Limited 1997 - DTC P0140 - HEATED OXYGEN SENSOR (HO2S) NO. 2 BANK 1/INSUFFICIENT ACTIVITY

NOTE:

ALWAYS inspect a faulty HO2S for contamination and correct cause before installing a new HO2S.

Isuzu Trooper Limited 1997 - Diagnostic Aids

An intermittent may be caused by a poor connection, rubbed through wire insulation or a broken wire inside insulation. Inspect harness connectors for backed out terminals, improper mating, broken locks, improperly formed or damaged terminals, poor terminal-to-wire connection, and damaged harness.

Using scan tool, monitor signal voltage while wiggling HO2S related connectors and wiring harness with a warm engine running at part throttle in closed loop. If a failure is induced, signal voltage will change from normal fluctuating voltage to a fixed voltage. A change in voltage will assist in isolating location of fault. DO NOT solder HO2S wires.

1. Perform On-Board Diagnostic (OBD) System Check. See BASIC TESTING article. Go to next step.
2. Start engine and allow it to reach normal operating temperature. Apply parking brake and increase engine speed to greater than 1200 RPM for 2 minutes. Using scan tool, observe HO2S No. 2, bank 1 parameter. If reading does not vary outside 425-475 mV range, go to step 4). If reading varies outside 425-475 mV range, turn engine off and go to next step.
3. Turn ignition on. Review and record FAILURE RECORDS data on scan tool. Operate vehicle within FAILURE RECORDS conditions. If DTC P0140 is set, go to next step. If DTC P0140 is not set, check for an intermittent problem, see DIAGNOSTIC AIDS .
4. Check for poor high or low signal circuit connections at HO2S No. 2, bank 1 harness connector or damaged harness. Repair as necessary. Retest system. If connection is okay, go to next step.
5. Turn ignition off. Disconnect PCM harness connectors. Check for poor HO2S No. 2, bank 1 high or low signal circuit connections at PCM harness connectors or damaged harness. Repair as necessary. Retest system. If connections are okay, go to next step.
6. Turn ignition off. Using an ohmmeter, measure resistance of HO2S No. 2, bank 1 high and low signal circuits between PCM and HO2S. If resistance is greater than 5 ohms in either wire, repair open or poor connection. Retest system. If wire is okay, go to next step.
7. Turn ignition on. Disconnect HO2S No. 2, bank 1 connector. Using a fused jumper wire, connect high and low signal circuit of HO2S No. 2, bank 1 (PCM side) to ground. If scan tool display is 0-10 mV, replace HO2S No. 2, bank 1. If display is not as specified, replace PCM. Retest system.

Isuzu Trooper Limited 1997 - DTC P0141 - HEATED OXYGEN SENSOR (HO2S) NO. 2 BANK 1/HEATER CIRCUIT

NOTE:

ALWAYS inspect a faulty HO2S for contamination and correct cause before installing a new HO2S.

Isuzu Trooper Limited 1997 - Diagnostic Aids

An intermittent may be caused by a poor connection, rubbed through wire insulation or a broken wire inside insulation. Inspect harness connectors for backed out terminals, improper mating, broken locks, improperly formed or damaged terminals, poor terminal-to-wire connection, and damaged harness. If DTC cannot be duplicated, check scan tool FAILURE RECORDS to determine mileage since last DTC was set.

1. Perform On-Board Diagnostic (OBD) System Check. See BASIC TESTING article. Go to next step.
2. Allow engine to cool. Disconnect fuel pump relay. Connect fused jumper between fuel pump relay socket positive battery terminal and relay wire that goes to fuel pump and HO2S fuses. Turn ignition off. Install scan tool. Turn ignition on. Observe HO2S No. 2, bank 1 parameter on scan tool. If display is greater than 650 mV or less than 250 mV, check for an intermittent problem, see DIAGNOSTIC AIDS . If display is not as specified, go to next step.
3. Inspect HO2S heater fuse (20-amp) in engine compartment fuse box. If fuse is blown, check for short in circuit and replace fuse. Retest system. If fuse is okay, go to next step.
4. Turn ignition off. Raise and support vehicle. Disconnect HO2S No. 2, bank 1 harness connector. Turn ignition on. Using a test light connected to ground, probe ignition feed circuit at connector (PCM side). If test light does not come on, go to step 7). If test light comes on, go to next step.
5. Connect test light between ignition feed circuit and ground circuit at connector (PCM side). If test light does not come on, go to step 8). If test light comes on, go to next step.
6. Turn ignition off. Ensure HO2S No. 2 is cool. Using an ohmmeter, measure resistance between ignition feed circuit and ground circuit at HO2S No. 2 harness connector (sensor side). If resistance is 3-6 ohms, go to step 9). If resistance is not as specified, go to step 10).
7. Repair open in HO2S No. 2 ignition feed circuit. Retest system.
8. Repair open in HO2S No. 2 ground circuit. Retest system.
9. Check for poor connection at HO2S No. 2, bank 1 harness terminals. Repair as necessary. Retest system. If harness is okay, go to next step.
10. Check for poor connection at HO2S No. 2, bank 1 high or low signal circuit terminal connections at harness connector. Repair as necessary. Retest system. If connections are okay, go to next step.
11. Turn ignition off. Disconnect PCM harness connector terminals. Using an ohmmeter, measure resistance of HO2S No. 2, bank 1 high and low signal circuits at PCM harness connector. If either circuit resistance is greater than 5 ohms, check for an open or poor connection. Repair as necessary. If wires are okay, go to next step.
12. Check for poor HO2S No. 2, bank 1 terminal connections at PCM. Repair as necessary. If connections are okay, replace HO2S No. 2, bank 1. Retest system.

Isuzu Trooper Limited 1997 - DTC P0143 - HEATED OXYGEN SENSOR (HO2S) NO. 3 BANK 1/LOW VOLTAGE

NOTE:

ALWAYS inspect a faulty HO2S for contamination and correct cause before installing a new HO2S.

Isuzu Trooper Limited 1997 - Diagnostic Aids

Check for sensor pigtail contacting exhaust system. Ensure PCM grounds are okay. Check fuel pressure. Perform INJECTOR BALANCE TEST. See FUEL SYSTEM in appropriate SYSTEM/COMPONENT TESTS article. Check vacuum hoses for leaks at intake, throttle body, PCV and EGR systems. Inspect exhaust system for leaks. MAF sensor can go lean, disconnect MAF and recheck.

1. Perform On-Board Diagnostic (OBD) System Check. See BASIC TESTING article. Go to next step.
2. Start engine and allow it to reach normal operating temperature. Ensure no related DTCs are present. Observe HO2S No. 3, bank 1 parameter on scan tool. If display is not as specified, go to next step. If display remains less than 22 mV, go to step 4).
3. Turn ignition on. Review and record FAILURE RECORDS data on scan tool. Operate vehicle within FAILURE RECORDS conditions. If DTC P0143 is set, go to next step. If DTC P0143 is not set, check for an intermittent problem, see DIAGNOSTIC AIDS .
4. Turn ignition off. Disconnect PCM harness connectors. Using an ohmmeter, check HO2S No. 3, bank 1 high and low signal circuits for a short to ground or HO2S heater ground circuit. Repair as necessary. Retest system. If wires are okay, go to next step.
5. Disconnect HO2S No. 3, bank 1 harness connector. Check HO2S No. 3, bank 1 high and low signal circuits for a short together. Repair as necessary. Retest system. If wires are okay, go to next step.
6. Reconnect PCM harness connectors, leaving HO2S No. 3 disconnected. Turn ignition on. Using scan tool, observe HO2S No. 3, bank 1 parameter. If display is 425-475 mV, replace HO2S No. 3. If display is not as specified, replace PCM. Retest system.

Isuzu Trooper Limited 1997 - DTC P0144 - HEATED OXYGEN SENSOR (HO2S) NO. 3 BANK 1/HIGH VOLTAGE

NOTE:

ALWAYS inspect a faulty HO2S for contamination and correct cause before installing a new HO2S.

Isuzu Trooper Limited 1997 - Diagnostic Aids

Check fuel pressure. Perform INJECTOR BALANCE TEST. See FUEL SYSTEM in appropriate SYSTEM/COMPONENT TESTS article. Check for leaking fuel pressure regulator by removing vacuum hose and checking for fuel presence. If fuel is present, replace regulator.

Check EVAP canister for fuel saturation. Check TP sensor. See SYSTEM/COMPONENT TESTS article. MAF sensor can go rich, disconnect MAF and recheck.

1. Perform On-Board Diagnostic (OBD) System Check. See BASIC TESTING article. Go to next step.
2. Start engine and allow it to reach normal operating temperature. Observe HO2S No. 3, bank 1 parameter on scan tool. If display remains greater than 952 mV, go to step 4). If display is not as specified, go to next step.
3. Turn ignition on. Review and record FAILURE RECORDS data on scan tool. Operate vehicle within FAILURE RECORDS conditions. If DTC P0144 is set, go to next step. If DTC P0144 is not set, check for an intermittent problem, see DIAGNOSTIC AIDS .
4. Turn ignition off. Disconnect HO2S No. 3, bank 1. Turn ignition on. Using a voltmeter, measure voltage of high and low signal circuits at harness connector (PCM side). If reading is 3-4 volts at either wire, repair signal circuit for short to power. If reading is not as specified, go to next step.
5. Turn ignition on. With HO2S No. 3, bank 1 disconnected, jumper high and low signal circuits at connector (PCM side) to ground. If display on scan tool is less than 10 mV, go to next step. If reading is not as specified, replace PCM. Retest system.
6. Disconnect jumpers. With HO2S connector disconnected, observe HO2S No. 3, bank 1 parameter on scan tool. If voltage is, 425-475 mV, check for an intermittent problem, see DIAGNOSTIC AIDS . If reading is not as specified, replace PCM. Retest system.

Isuzu Trooper Limited 1997 - DTC P0146 - HEATED OXYGEN SENSOR (HO2S) NO. 3 BANK 1/INSUFFICIENT ACTIVITY

NOTE:

ALWAYS inspect a faulty HO2S for contamination and correct cause before installing a new HO2S.

Isuzu Trooper Limited 1997 - Diagnostic Aids

An intermittent may be caused by a poor connection, rubbed through wire insulation or a broken wire inside insulation. Inspect harness connectors for backed out terminals, improper mating, broken locks, improperly formed or damaged terminals, poor terminal-to-wire connection, and damaged harness.

Using scan tool, monitor signal voltage while wiggling HO2S related connectors and wiring harness with a warm engine running at part throttle in closed loop. If a failure is induced, signal voltage will change from normal fluctuating voltage to a fixed voltage. A change in voltage will assist in isolating location of fault. DO NOT solder HO2S wires.

1. Perform On-Board Diagnostic (OBD) System Check. See BASIC TESTING article. Go to next step.
2. Start engine and allow it to reach normal operating temperature. Apply parking brake and increase engine speed to greater than 1200 RPM for 2 minutes. Using scan tool, observe HO2S No. 3, bank 1 parameter. If reading does not vary outside 425-475 mV range, go to step 4). If reading varies outside 425-475 mV range, turn engine off and go to next step.
3. Turn ignition on. Review and record FAILURE RECORDS data on scan tool. Operate vehicle within FAILURE RECORDS conditions. If DTC P0146 is set, go to next step. If DTC P0146 is not set, check for an intermittent problem, see DIAGNOSTIC AIDS .
4. Check for poor high or low signal circuit connections at HO2S No. 3, bank 1 harness connector or damaged harness. Repair as necessary. Retest system. If connection is okay, go to next step.
5. Turn ignition off. Disconnect PCM harness connectors. Check for poor HO2S No. 3, bank 1 high or low signal circuit connections at PCM harness connectors or damaged harness. Repair as necessary. Retest system. If connections are okay, go to next step.
6. Turn ignition off. Using an ohmmeter, measure resistance of HO2S No. 3, bank 1 high and low signal circuits between PCM and HO2S. If resistance is greater than 5 ohms in either wire, repair open or poor connection. Retest system. If wire is okay, go to next step.
7. Turn ignition on. Disconnect HO2S No. 3, bank 1 connector. Using a fused jumper wire, connect high and low signal circuit of HO2S No. 3, bank 1 (PCM side) to ground. If scan tool display is 0-10 mV, replace HO2S No. 3, bank 1. If display is not as specified, replace PCM. Retest system.

Isuzu Trooper Limited 1997 - DTC P0147 - HEATED OXYGEN SENSOR (HO2S) NO. 3 BANK 1/HEATER CIRCUIT

NOTE:

ALWAYS inspect a faulty HO2S for contamination and correct cause before installing a new HO2S.

Isuzu Trooper Limited 1997 - Diagnostic Aids

An intermittent may be caused by a poor connection, rubbed through wire insulation or a broken wire inside insulation. Inspect harness connectors for backed out terminals, improper mating, broken locks, improperly formed or damaged terminals, poor terminal-to-wire connection, and damaged harness. If DTC cannot be duplicated, check scan tool FAILURE RECORDS to determine mileage since last DTC was set.

1. Perform On-Board Diagnostic (OBD) System Check. See BASIC TESTING article. Go to next step.
2. Allow engine to cool. Disconnect fuel pump relay. Connect fused jumper between fuel pump relay socket positive battery terminal and relay wire that goes to fuel pump and HO2S fuses. Turn ignition off. Install scan tool. Turn ignition on. Observe HO2S No. 3, bank 1 parameter on scan tool. If display is greater than 650 mV or less than 250 mV, check for an intermittent problem, see DIAGNOSTIC AIDS . If display is not as specified, go to next step.
3. Inspect HO2S heater fuse (20-amp) in engine compartment fuse box. If fuse is blown, check for short in circuit and replace fuse. Retest system. If fuse is okay, go to next step.
4. Turn ignition off. Raise and support vehicle. Disconnect HO2S No. 3, bank 1 harness connector. Turn ignition on. Using a test light connected to ground, probe ignition feed circuit at connector (PCM side). If test light does not come on, go to step 7). If test light comes on, go to next step.
5. Connect test light between ignition feed circuit and ground circuit at connector (PCM side). If test light does not come on, go to step 8). If test light comes on, go to next step.
6. Turn ignition off. Ensure HO2S No. 3 is cool. Using an ohmmeter, measure resistance between ignition feed circuit and ground circuit at HO2S No. 3 harness connector (sensor side). If resistance is 3-6 ohms, go to step 9). If resistance is not as specified, go to step 10).
7. Repair open in HO2S No. 3 ignition feed circuit. Retest system.
8. Repair open in HO2S No. 3 ground circuit. Retest system.
9. Check for poor connection at HO2S No. 3, bank 1 harness terminals. Repair as necessary. Retest system. If harness is okay, go to next step.
10. Check for poor connection at HO2S No. 3, bank 1 high or low signal circuit terminal connections at harness connector. Repair as necessary. Retest system. If connections are okay, go to next step.
11. Turn ignition off. Disconnect PCM harness connector terminals. Using an ohmmeter, measure resistance of HO2S No. 3, bank 1 high and low signal circuits at PCM harness connector. If either circuit resistance is greater than 5 ohms, check for an open or poor connection. Repair as necessary. If wires are okay, go to next step.
12. Check for poor HO2S No. 3, bank 1 terminal connections at PCM. Repair as necessary. If connections are okay, replace HO2S No. 3, bank 1. Retest system.

Isuzu Trooper Limited 1997 - DTC P0151 - HEATED OXYGEN SENSOR (HO2S) NO. 1 BANK 2/LOW VOLTAGE

NOTE:

ALWAYS inspect a faulty HO2S for contamination and correct cause before installing a new HO2S.

Isuzu Trooper Limited 1997 - Diagnostic Aids

Check for HO2S pigtail wire for breaks, contamination or grounding on exhaust manifold. Check for intermittent ground in signal wire between sensor connector and sensor.

Check for lean injector(s). Perform Injector Balance Test. See SYSTEM/COMPONENT TESTS article. Check for fuel contamination, improper fuel pressure or exhaust leak, especially near HO2S. Check for vacuum or crankcase leak, causing a lean condition.

1. Perform On-Board Diagnostic (OBD) System Check. See BASIC TESTING article. Go to next step.
2. Start engine and allow it to reach normal operating temperature. Using scan tool, observe HO2S No. 1, bank 2 parameter on scan tool. If display remains less than 22 mV, go to step 4). If display is not as specified, go to next step.
3. Turn ignition on. Review and record FAILURE RECORDS data on scan tool. Operate vehicle within FAILURE RECORDS conditions. If DTC P0151 is set, go to next step. If DTC P0151 is not set, check for an intermittent problem, see DIAGNOSTIC AIDS .
4. Turn ignition off. Disconnect PCM harness connectors. Using an ohmmeter, check HO2S No. 1, bank 2 high and low circuits for a short to ground or short to heater ground circuit. Repair as necessary. Retest system. If wires are okay, go to next step.
5. Disconnect HO2S No. 1, bank 2 harness connector. Using an ohmmeter, check for continuity between high and low signal circuits at harness connector. If continuity is present, check for short between wires and repair as necessary. Retest system. If continuity is not present, go to next step.
6. Reconnect PCM, leaving sensor disconnected. Turn ignition on. If HO2S No. 1, bank 2 parameter on scan tool is 425-475 mV, check for an intermittent problem, see DIAGNOSTIC AIDS . If reading is not as specified, replace PCM. Retest system.

Isuzu Trooper Limited 1997 - DTC P0152 - HEATED OXYGEN SENSOR (HO2S) NO. 1 BANK 2/HIGH VOLTAGE

NOTE:

ALWAYS inspect a faulty HO2S for contamination and correct cause before installing a new HO2S.

Isuzu Trooper Limited 1997 - Diagnostic Aids

Check fuel pressure. Perform INJECTOR BALANCE TEST. See FUEL SYSTEM in appropriate SYSTEM/COMPONENT TESTS article. Check for leaking fuel pressure regulator by removing vacuum hose and checking for fuel presence. If fuel is present, replace regulator. Check EVAP canister for fuel saturation. Check MAF sensor. Check TP sensor. See SYSTEM/COMPONENT TESTS article.

1. Perform On-Board Diagnostic (OBD) System Check. See BASIC TESTING article. Go to next step.
2. Start engine and allow it to reach normal operating temperature. Using scan tool, observe HO2S No. 1, bank 2 parameter. If display remains greater than 952 mV, go to step 4). If display is not as specified, go to next step.
3. Turn ignition on. Review and record FAILURE RECORDS data on scan tool. Operate vehicle within FAILURE RECORDS conditions. If DTC P0152 is set, go to next step. If DTC P0152 is not set, check for an intermittent problem, see DIAGNOSTIC AIDS .
4. Turn ignition off. Disconnect HO2S No. 1, bank 2. Turn ignition on. Using a voltmeter, measure voltage of high and low signal circuits at harness connector (PCM side). If reading is 3-4 volts at either wire, repair signal circuit for short to power. If reading is not as specified, go to next step.
5. Turn ignition on. Jumper high and low signal circuits of connector (PCM side) to ground. If display on scan tool is less than 10 mV, go to next step. If reading is not as specified, replace PCM. Retest system.
6. Disconnect jumper from signal circuits. Using scan tool, observe replace HO2S No. 1, bank 2 parameter. If display remains is 425-475 mV, see DIAGNOSTIC AIDS . If display remains is not 425-475 mV, replace PCM. Retest system.

Isuzu Trooper Limited 1997 - DTC P0153 - HEATED OXYGEN SENSOR (HO2S) NO. 1 BANK 2/SLOW RESPONSE

NOTE:

ALWAYS inspect a faulty HO2S for contamination and correct cause before installing a new HO2S.

NOTE:

If any DTCs are set (except for P0133, P1133, P1134, P1153 and/or P1154), diagnose them first.

Isuzu Trooper Limited 1997 - Diagnostic Aids

An intermittent problem can be caused by misrouted harness, rubbed-through wire insulation or broken wire inside insulation. If DTC cannot be duplicated, check scan tool FAILURE RECORDS to determine mileage since last DTC was set.

1. Perform On-Board Diagnostic (OBD) System Check. See BASIC TESTING article. Go to next step.
2. Start engine and allow it to reach operating temperature. Operate vehicle within conditions required to set DTC:
   • Engine in closed loop.
   • Engine running for one minute or more.
   • Engine RPM is 1500-3000.
   • Canister purge duty cycle is 2 percent or more.
   • MAF is 9-42 grams per second.
   • All conditions for 3 seconds or more.
   • Rich-to-lean transition is longer than 105 milliseconds.
   • Lean-to-Rich transition is longer than 94 milliseconds.

   Using scan tool, observe SPECIFIC DTC parameter. If scan tool displays DTC P0153 FAILED THIS IGN, go to next step. If scan tool does not display DTC P0153 FAILED THIS IGN, check for an intermittent problem, see DIAGNOSTIC AIDS .

3. If scan tool also displays DTC P0153, P1133, P1134, P1153 and/or P1154 FAILED THIS IGN, replace affected HO2S. Retest system. If scan tool does not display these DTCs, go to next step.
4. Visually inspect exhaust system for leaks near HO2S No. 1, bank 2. If leaks are found, repair as necessary and return to step 2). If no leaks are found, go to next step.
5. Visually inspect HO2S No. 1, bank 2 for proper installation. Check for corrosion on terminals. Check terminal tension at HO2S No. 1, bank 2 and PCM. Repair as necessary. If no problem is found, go to next step.
6. Disconnect HO2S No. 1, bank 2 harness connector. Using a voltmeter, measure voltage between high signal circuit and ground, then low signal circuit and ground. If reading is 3-4 volts, go to next step. If reading is not as specified, go to step 8).
7. Using a fused jumper wire, connect high and low signal circuits of HO2S No. 1, bank 2 harness connector (PCM side) to ground. Turn ignition on. Using scan tool, monitor voltage. If reading is less than 10 mV and immediately returns to about 450 mV when jumper wire is removed, replace HO2S No. 1, bank 2. If reading is not as specified, replace PCM. Retest system.
8. Inspect PCM connections and terminals for damage. Repair as necessary. Retest system. If PCM connections and terminals are okay, go to next step.
9. Repair open, short or grounded HO2S No. 1, bank 2 high or low signal circuits. Retest system.

Isuzu Trooper Limited 1997 - DTC P0154 - HEATED OXYGEN SENSOR (HO2S) NO. 1 BANK 2/INSUFFICIENT ACTIVITY

NOTE:

ALWAYS inspect a faulty HO2S for contamination and correct cause before installing a new HO2S.

Isuzu Trooper Limited 1997 - Diagnostic Aids

An intermittent may be caused by a poor connection, rubbed through wire insulation or a broken wire inside insulation. Inspect harness connectors for backed out terminals, improper mating, broken locks, improperly formed or damaged terminals, poor terminal-to-wire connection, and damaged harness.

Using scan tool, monitor signal voltage while wiggling HO2S related connectors and wiring harness with a warm engine running at part throttle in closed loop. If a failure is induced, signal voltage will change from normal fluctuating voltage to a fixed voltage. A change in voltage will assist in isolating location of fault. DO NOT solder HO2S wires.

1. Perform On-Board Diagnostic (OBD) System Check. See BASIC TESTING article. Go to next step.
2. Start engine and allow it to reach normal operating temperature. Apply parking brake and increase engine speed to greater than 1200 RPM for 2 minutes. Using scan tool, observe HO2S No. 1, bank 2 parameter. If reading varies outside 400-500 mV range, turn engine off and go to next step. If reading does not vary outside 400-500 mV range, go to step 4).
3. Turn ignition on. Review and record FAILURE RECORDS data on scan tool. Operate vehicle within FAILURE RECORDS conditions. If DTC P0154 is set, go to next step. If DTC P0154 is not set, check for an intermittent problem, see DIAGNOSTIC AIDS .
4. Inspect sensor harness for damage. Repair as necessary. If harness is okay, go to next step.
5. Check for poor signal circuit connections at HO2S No. 1, bank 2 harness connector. Repair as necessary. Retest system. If connection is okay, go to next step.
6. Check for poor HO2S No. 1, bank 2 signal circuit connections at PCM harness connectors. Repair as necessary. Retest system. If connections are okay, go to next step.
7. Turn ignition off. Disconnect PCM connectors. Using an ohmmeter, measure resistance of HO2S No. 1, bank 2 high signal circuit between PCM and HO2S. If resistance is greater than 5 ohms, repair open or poor connection. Retest system. If wire is okay, go to next step.
8. Measure resistance of HO2S No. 1, bank 2 low signal circuit between PCM and HO2S. If resistance is greater than 5 ohms, repair open or poor connection. Retest system. If wire is okay, reconnect PCM connectors and go to next step.
9. Disconnect HO2S No. 1, bank 2 connector. Turn ignition on. Using a fused jumper wire, connect high and low signal circuits of HO2S No. 1, bank 2 (PCM side) to ground. If scan tool display is 0-10 mV, replace HO2S No. 1, bank 2. If display is not as specified, replace PCM. Retest system.

Isuzu Trooper Limited 1997 - DTC P0155 - HEATED OXYGEN SENSOR (HO2S) NO. 1 BANK 2/HEATER CIRCUIT

NOTE:

ALWAYS inspect a faulty HO2S for contamination and correct cause before installing a new HO2S.

Isuzu Trooper Limited 1997 - Diagnostic Aids

An intermittent may be caused by a poor connection, rubbed through wire insulation or a broken wire inside insulation. Inspect harness connectors for backed out terminals, improper mating, broken locks, improperly formed or damaged terminals, poor terminal-to-wire connection, and damaged harness. If DTC cannot be duplicated, check scan tool FAILURE RECORDS to determine mileage since last DTC was set.

1. Perform On-Board Diagnostic (OBD) System Check. See BASIC TESTING article. Go to next step.
2. Allow engine to cool. Disconnect fuel pump relay. Connect fused jumper between fuel pump relay socket positive battery terminal and relay wire that goes to fuel pump and HO2S. Turn ignition off. Install scan tool. Turn ignition on. Observe HO2S No. 1, bank 2 parameter on scan tool for several minutes. If display is greater than 650 mV or less than 250 mV, check for an intermittent problem, see DIAGNOSTIC AIDS . If display is not as specified, go to next step.
3. Inspect HO2S heater fuse (20-amp) in engine compartment fuse box. If fuse is blown, check for short in circuit and replace fuse. Retest system. If fuse is okay, go to next step.
4. Turn ignition off. Raise and support vehicle. Disconnect HO2S No. 1, bank 2 harness connector. Turn ignition on. Using a test light connected to ground, probe ignition feed circuit at connector (PCM side). If test light comes on, go to next step. If test light does not come on, go to step 7).
5. Connect test light between ignition feed circuit and ground circuit at connector (PCM side). If test light comes on, go to next step. If test light does not come on, go to step 8).
6. Turn ignition off. Ensure HO2S No. 1 is cool. Using an ohmmeter, measure resistance between ignition feed circuit and heater ground circuit at HO2S No. 1 harness connector (sensor side). If resistance is 3-6 ohms, go to step 9). If resistance is not as specified, go to step 10).
7. Repair open in HO2S No. 1 ignition feed circuit. Retest system.
8. Repair open in HO2S No. 1 ground circuit. Retest system.
9. Check for poor connection at HO2S No. 1, bank 2 harness terminals. Repair as necessary. Retest system. If harness is okay, go to next step.
10. Check for poor connection at HO2S No. 1, bank 2 high or low circuit terminal connections at harness connector. Repair as necessary. Retest system. If connections are okay, go to next step.
11. Turn ignition off. Disconnect PCM harness connector terminals. Using an ohmmeter, measure resistance of HO2S No. 1, bank 2 high and low signal circuits at PCM harness connector. If either circuit resistance is greater than 5 ohms, check for an open or poor connection. Repair as necessary. If wires are okay, go to next step.
12. Check for poor HO2S No. 1, bank 2 terminal connections at PCM. Repair as necessary. If connections are okay, replace HO2S No. 1, bank 2. Retest system.

Isuzu Trooper Limited 1997 - DTC P0157 - HEATED OXYGEN SENSOR (HO2S) NO. 2 BANK 2/LOW VOLTAGE

NOTE:

ALWAYS inspect a faulty HO2S for contamination and correct cause before installing a new HO2S.

Isuzu Trooper Limited 1997 - Diagnostic Aids

Check for HO2S pigtail wire for breaks, contamination or grounding on exhaust manifold. Check for intermittent ground in signal wire between sensor connector and sensor.

Check for lean injector(s). Perform Injector Balance Test. See SYSTEM/COMPONENT TESTS article. Check for fuel contamination, improper fuel pressure or exhaust leak, especially near HO2S. Check for vacuum or crankcase leak, causing a lean condition.

1. Perform On-Board Diagnostic (OBD) System Check. See BASIC TESTING article. Go to next step.
2. Start engine and allow it to reach normal operating temperature. Using scan tool, observe HO2S No. 2, bank 2 parameter on scan tool. If display remains less than 22 mV, go to step 4). If display is not as specified, go to next step.
3. Turn ignition on. Review and record FAILURE RECORDS data on scan tool. Operate vehicle within FAILURE RECORDS conditions. If DTC P0157 is set, go to next step. If DTC P0157 is not set, check for an intermittent problem, see DIAGNOSTIC AIDS .
4. Turn ignition off. Disconnect PCM harness connectors. Using an ohmmeter, check HO2S No. 2, bank 2 high and low circuits for a short to ground or short to heater ground circuit. Repair as necessary. Retest system. If wires are okay, go to next step.
5. Disconnect HO2S No. 2, bank 2 harness connector. Using an ohmmeter, check for continuity between high and low signal circuits at harness connector. If continuity is present, check for short between wires and repair as necessary. Retest system. If continuity is not present, go to next step.
6. Reconnect PCM, leaving sensor disconnected. Turn ignition on. If HO2S No. 2, bank 2 parameter on scan tool is 425-475 mV, check for an intermittent problem, see DIAGNOSTIC AIDS . If reading is not as specified, replace PCM. Retest system.

Isuzu Trooper Limited 1997 - DTC P0158 - HEATED OXYGEN SENSOR (HO2S) NO. 2 BANK 2/HIGH VOLTAGE

NOTE:

ALWAYS inspect a faulty HO2S for contamination and correct cause before installing a new HO2S.

Isuzu Trooper Limited 1997 - Diagnostic Aids

Check fuel pressure. Perform INJECTOR BALANCE TEST. See FUEL SYSTEM in appropriate SYSTEM/COMPONENT TESTS article. Check for leaking fuel pressure regulator by removing vacuum hose and checking for fuel presence. If fuel is present, replace regulator. Check EVAP canister for fuel saturation. Check MAF sensor. Check TP sensor. See SYSTEM/COMPONENT TESTS article.

1. Perform On-Board Diagnostic (OBD) System Check. See BASIC TESTING article. Go to next step.
2. Start engine and allow it to reach normal operating temperature. Using scan tool, observe HO2S No. 2, bank 2 parameter. If display remains greater than 952 mV, go to step 4). If display is not as specified, go to next step.
3. Turn ignition on. Review and record FAILURE RECORDS data on scan tool. Operate vehicle within FAILURE RECORDS conditions. If DTC P0158 is set, go to next step. If DTC P0158 is not set, check for an intermittent problem, see DIAGNOSTIC AIDS .
4. Turn ignition off. Disconnect HO2S No. 2, bank 2. Turn ignition on. Using a voltmeter, measure voltage of high and low signal circuits at harness connector (PCM side). If reading is 3-4 volts at either wire, repair signal circuit for short to power. If reading is not as specified, go to next step.
5. Turn ignition on. Jumper high and low signal circuits of connector (PCM side) to ground. If display on scan tool is less than 10 mV, go to next step. If reading is not as specified, replace PCM. Retest system.
6. Disconnect jumper from signal circuits. Using scan tool, observe replace HO2S No. 2, bank 2 parameter. If display remains is 425-475 mV, see DIAGNOSTIC AIDS . If display remains is not 425-475 mV, replace PCM. Retest system.

Isuzu Trooper Limited 1997 - DTC P0160 - HEATED OXYGEN SENSOR (HO2S) NO. 2 BANK 2/INSUFFICIENT ACTIVITY

NOTE:

ALWAYS inspect a faulty HO2S for contamination and correct cause before installing a new HO2S.

Isuzu Trooper Limited 1997 - Diagnostic Aids

An intermittent may be caused by a poor connection, rubbed through wire insulation or a broken wire inside insulation. Inspect harness connectors for backed out terminals, improper mating, broken locks, improperly formed or damaged terminals, poor terminal-to-wire connection, and damaged harness.

Using scan tool, monitor signal voltage while wiggling HO2S related connectors and wiring harness with a warm engine running at part throttle in closed loop. If a failure is induced, signal voltage will change from normal fluctuating voltage to a fixed voltage. A change in voltage will assist in isolating location of fault. DO NOT solder HO2S wires.

1. Perform On-Board Diagnostic (OBD) System Check. See BASIC TESTING article. Go to next step.
2. Start engine and allow it to reach normal operating temperature. Apply parking brake and increase engine speed to greater than 1200 RPM for 2 minutes. Using scan tool, observe HO2S No. 2, bank 2 parameter. If reading varies outside 425-475 mV range, turn engine off and go to next step. If reading does not vary outside 425-475 mV range, go to step 4).
3. Turn ignition on. Review and record FAILURE RECORDS data on scan tool. Operate vehicle within FAILURE RECORDS conditions. If DTC P0160 is set, go to next step. If DTC P0160 is not set, check for an intermittent problem, see DIAGNOSTIC AIDS .
4. Inspect sensor harness for damage. Repair as necessary. If harness is okay, go to next step.
5. Check for poor signal circuit connections at HO2S No. 2, bank 2 harness connector. Repair as necessary. Retest system. If connection is okay, go to next step.
6. Check for poor HO2S No. 2, bank 2 signal circuit connections at PCM harness connectors. Repair as necessary. Retest system. If connections are okay, go to next step.
7. Turn ignition off. Disconnect PCM connectors. Using an ohmmeter, measure resistance of HO2S No. 2, bank 2 high signal circuit between PCM and HO2S. If resistance is greater than 5 ohms, repair open or poor connection. Retest system. If wire is okay, go to next step.
8. Measure resistance of HO2S No. 2, bank 2 low signal circuit between PCM and HO2S. If resistance is greater than 5 ohms, repair open or poor connection. Retest system. If wire is okay, reconnect PCM connectors and go to next step.
9. Disconnect HO2S No. 2, bank 2 connector. Turn ignition on. Using a fused jumper wire, connect high and low signal circuits of HO2S No. 2, bank 2 (PCM side) to ground. If scan tool display is 0-10 mV, replace HO2S No. 2, bank 2. If display is not as specified, replace PCM. Retest system.

Isuzu Trooper Limited 1997 - DTC P0161 - HEATED OXYGEN SENSOR (HO2S) NO. 2 BANK 2/HEATER CIRCUIT

NOTE:

ALWAYS inspect a faulty HO2S for contamination and correct cause before installing a new HO2S.

Isuzu Trooper Limited 1997 - Diagnostic Aids

An intermittent may be caused by a poor connection, rubbed through wire insulation or a broken wire inside insulation. Inspect harness connectors for backed out terminals, improper mating, broken locks, improperly formed or damaged terminals, poor terminal-to-wire connection, and damaged harness. If DTC cannot be duplicated, check scan tool FAILURE RECORDS to determine mileage since last DTC was set.

1. Perform On-Board Diagnostic (OBD) System Check. See BASIC TESTING article. Go to next step.
2. Allow engine to cool. Disconnect fuel pump relay. Connect fused jumper between fuel pump relay socket positive battery terminal and relay wire that goes to fuel pump and HO2S. Turn ignition off. Install scan tool. Turn ignition on. Observe HO2S No. 2, bank 2 parameter on scan tool for several minutes. If display is greater than 650 mV or less than 250 mV, check for an intermittent problem, see DIAGNOSTIC AIDS . If display is not as specified, go to next step.
3. Inspect HO2S heater fuse (20-amp) in engine compartment fuse box. If fuse is blown, check for short in circuit and replace fuse. Retest system. If fuse is okay, go to next step.
4. Turn ignition off. Raise and support vehicle. Disconnect HO2S No. 2, bank 2 harness connector. Turn ignition on. Using a test light connected to ground, probe ignition feed circuit at connector (PCM side). If test light comes on, go to next step. If test light does not come on, go to step 7).
5. Connect test light between ignition feed circuit and ground circuit at connector (PCM side). If test light comes on, go to next step. If test light does not come on, go to step 8).
6. Turn ignition off. Ensure HO2S No. 2 is cool. Using an ohmmeter, measure resistance between ignition feed circuit and heater ground circuit at HO2S No. 2 harness connector (sensor side). If resistance is 3-6 ohms, go to step 9). If resistance is not as specified, go to step 10).
7. Repair open in HO2S No. 2 ignition feed circuit. Retest system.
8. Repair open in HO2S No. 2 ground circuit. Retest system.
9. Check for poor connection at HO2S No. 2, bank 2 harness terminals. Repair as necessary. Retest system. If harness is okay, go to next step.
10. Check for poor connection at HO2S No. 2, bank 2 high or low circuit terminal connections at harness connector. Repair as necessary. Retest system. If connections are okay, go to next step.
11. Turn ignition off. Disconnect PCM harness connector terminals. Using an ohmmeter, measure resistance of HO2S No. 2, bank 2 high and low signal circuits at PCM harness connector. If either circuit resistance is greater than 5 ohms, check for an open or poor connection. Repair as necessary. If wires are okay, go to next step.
12. Check for poor HO2S No. 2, bank 2 terminal connections at PCM. Repair as necessary. If connections are okay, replace HO2S No. 2, bank 2. Retest system.

Isuzu Trooper Limited 1997 - DTC P0171 - BANK 1 SYSTEM TOO LEAN Diagnostic Aids

An intermittent may be caused by a poor connection, rubbed through wire insulation or a broken wire inside insulation. Inspect harness connectors for backed out terminals, improper mating, broken locks, improperly formed or damaged terminals, poor terminal-to-wire connection, and damaged harness. If DTC cannot be duplicated, check scan tool FAILURE RECORDS to determine mileage since last DTC was set.

1. Perform On-Board Diagnostic (OBD) System Check. Read and record FREEZE FRAME and/or FAIL RECORDS data for each DTC set. Go to next step.
2. If any DTCs other than P0171 and P0174 are set, diagnose them first before proceeding. If no other DTCs are set, go to next step.
3. Operate vehicle in closed loop mode while using scan tool to read BANK 1 L.T. FUEL TRIM values. If L.T. FUEL TRIM value is more than 20 percent, go to step 5). If value is not as specified, go to next step.
4. Using scan tool, read and record FAIL RECORDS data. Clear DTCs and operate vehicle within FAILURE RECORDS conditions. If DTC P0171 is set, go to next step. If DTC P0171 is not set, check for an intermittent problem, see DIAGNOSTIC AIDS .
5. If DTC P0174 is also set, go to next step. If DTC P0174 is not set, go to step 15).
6. Check vacuum hoses for splits, kinks and proper routing. If a problem is found, repair as necessary. Retest system. If no problem is found, go to next step.
7. Check PCV valve for proper installation. If a problem is found, repair as necessary. Retest system. If no problem is found, go to next step.
8. Check MAF inlet screen for blockage or foreign objects which may partially block airflow sample through MAF sensor. If a problem is found, repair as necessary. Retest system. If no problem is found, go to next step.
9. Start engine. If a high or unsteady idle condition exists, go to next step. If Idle is okay, go to step 11).
10. Check throttle body, intake manifold, and EGR valve for vacuum leaks. If a problem is found, repair as necessary. Retest system. If no problem is found, go to next step.
11. Check for fuel contamination. If fuel is contaminated, repair as necessary. Retest system. If fuel is okay, go to next step.
12. Check PCM injector, power and sensor ground circuits for clean and tight connections. If a problem is found, repair as necessary. Retest system. If no problem is found, go to next step.
13. Disconnect MAF sensor harness connector. Operate vehicle in closed loop mode while monitoring scan tool BANK 1 S.T. FUEL TRIM. If S.T. FUEL TRIM does not decrease to about zero percent, go to next step. If S.T. FUEL TRIM decreases to about zero percent, go to step 19).
14. Perform FUEL SYSTEM PRESSURE TEST under BASIC FUEL SYSTEM CHECKS in appropriate BASIC TESTING article. If a problem is found, repair as necessary. Retest system. If no problem is found, go to next step.
15. Check intake manifold, injector "O" rings, EGR adapter, EGR valve and EGR feed pipes for vacuum leaks. If a problem is found, repair as necessary. Retest system. If no problem is found, go to next step.
16. Check exhaust system for corrosion, loose or missing hardware. If a problem is found, repair as necessary. Retest system. If no problem is found, go to next step.
17. Perform, INJECTOR BALANCE TEST. See FUEL SYSTEM in SYSTEM/COMPONENT TESTS article. If a problem is found, repair as necessary. Retest system. If no problem is found, go to next step.
18. Ensure HO2S is installed securely, and connector and harness are not contacting exhaust manifold or ignition wires. If a problem is found, repair as necessary. Retest system. If no problem is found, check for an intermittent problem, see DIAGNOSTIC AIDS .
19. Replace MAF sensor. Retest system.

Isuzu Trooper Limited 1997 - DTC P0172 - BANK 1 SYSTEM TOO RICH Diagnostic Aids

An intermittent may be caused by a poor connection, rubbed through wire insulation or a broken wire inside insulation. Inspect harness connectors for backed out terminals, improper mating, broken locks, improperly formed or damaged terminals, poor terminal-to-wire connection, and damaged harness. If DTC cannot be duplicated, check scan tool FAILURE RECORDS to determine mileage since last DTC was set.

1. Perform On-Board Diagnostic (OBD) System Check. Read and record FREEZE FRAME and/or FAIL RECORDS data for each DTC set. Go to next step.
2. If any other DTCs are set, diagnose affected DTCs before proceeding. If no other DTCs are set, go to next step.
3. Operate vehicle in closed loop mode while using scan tool to read BANK 1 L.T. FUEL TRIM values. If L.T. FUEL TRIM value is less than -15 percent for auto trans and is less than -12 percent for manual trans, go to step 5). If values are not as specified, go to next step.
4. Using scan tool, read and record FAIL RECORDS data. Clear DTCs and operate vehicle within FAILURE RECORDS conditions. If DTC P0172 is set, go to next step. If DTC P0172 is not set, check for an intermittent problem, see DIAGNOSTIC AIDS .
5. If DTC P0175 is also set, go to next step. If DTC P0175 is not set, go to step 15).
6. Check air filter element condition. Replace air filter element if necessary. Retest system. If air filter element is okay, go to next step.
7. Check for collapsed or restricted air intake duct. If a problem is found, repair as necessary. Retest system. If no problem is found, go to next step.
8. Check MAF inlet screen for blockage or foreign objects which may partially block airflow sample through MAF sensor. If a problem is found, repair as necessary. Retest system. If no problem is found, go to next step.
9. Start engine. If a high or unsteady idle condition exists, go to next step. If Idle is okay, go to step 11).
10. Turn ignition off. Check throttle body bore and throttle plate for restriction or foreign objects. Check for clogged IAC passages. If a problem is found, repair as necessary. Retest system. If no problem is found, go to next step.
11. Disconnect vacuum hose from fuel pressure regulator and check it for presence of fuel. If fuel is present, replace fuel pressure regulator. Retest system. If no fuel is present, go to next step.
12. Turn ignition on. Using scan tool, read TP ANGLE while slowly depressing accelerator pedal. If TP ANGLE increases steadily from zero percent at closed throttle to 100 percent at wide open throttle, go to next step. If TP ANGLE does not increase as specified, go tostep 19).
13. Disconnect MAF sensor connector. Operate vehicle in closed loop mode while monitoring scan tool BANK 1 L.T. and BANK 1 S.T. FUEL TRIM. If both FUEL TRIM values decrease to about zero percent, go to step 20). If FUEL TRIM values do not decrease to about zero percent, go to next step.
14. Perform FUEL SYSTEM PRESSURE TEST. See BASIC TESTING article. If a problem is found, repair as necessary. Retest system. If no problem is found, go to next step.
15. Turn ignition on. Connect test light between canister purge solenoid connector terminals. If test light is on, go to next step. If test light is not on, replace PCM. Retest system.
16. Using an ohmmeter, check for continuity to ground in Red/Blue wire between PCM connector "A" terminal No. 15 and canister purge solenoid connector. See PIN VOLTAGE CHARTS . If continuity exists, repair short to ground. Retest system. If continuity to ground does not exist, go to next step.
17. Perform, INJECTOR BALANCE TEST. See FUEL SYSTEM in SYSTEM/COMPONENT TESTS article. If a problem is found, repair as necessary. Retest system. If no problem is found, go to next step.
18. Remove HO2S No. 1 and check for silicone contamination (powdery white deposit). If HO2S No. 1 is contaminated, replace HO2S No. 1. Retest system. If HO2S No. 1 is not contaminated, check for an intermittent problem, see DIAGNOSTIC AIDS .
19. Check for loose TP sensor mounting screws. Adjust TP sensor if necessary. If mounting screws are tight, replace TP sensor. Retest system.
20. Replace MAF sensor. Retest system.

Isuzu Trooper Limited 1997 - DTC P0174 - BANK 2 SYSTEM TOO LEAN Diagnostic Aids

An intermittent may be caused by a poor connection, rubbed through wire insulation or a broken wire inside insulation. Inspect harness connectors for backed out terminals, improper mating, broken locks, improperly formed or damaged terminals, poor terminal-to-wire connection, and damaged harness. If DTC cannot be duplicated, check scan tool FAILURE RECORDS to determine mileage since last DTC was set.

1. Perform On-Board Diagnostic (OBD) System Check. Read and record FREEZE FRAME and/or FAIL RECORDS data for each DTC set. Go to next step.
2. If any DTCs other than P0171 and P0174 are set, diagnose them first before proceeding. If no other DTCs are set, go to next step.
3. Operate vehicle in closed loop mode while using scan tool to read BANK 1 L.T. FUEL TRIM values. If L.T. FUEL TRIM value is more than 20 percent, go to step 5). If value is not as specified, go to next step.
4. Using scan tool, read and record FAIL RECORDS data. Clear DTCs and operate vehicle within FAILURE RECORDS conditions. If DTC P0174 is set, go to next step. If DTC P0174 is not set, check for an intermittent problem, see DIAGNOSTIC AIDS .
5. If DTC P0171 is also set, go to next step. If DTC P0171 is not set, go to step 15).
6. Check vacuum hoses for splits, kinks and proper routing. If a problem is found, repair as necessary. Retest system. If no problem is found, go to next step.
7. Check PCV valve for proper installation. If a problem is found, repair as necessary. Retest system. If no problem is found, go to next step.
8. Check MAF inlet screen for blockage or foreign objects which may partially block airflow sample through MAF sensor. If a problem is found, repair as necessary. Retest system. If no problem is found, go to next step.
9. Start engine. If a high or unsteady idle condition exists, go to next step. If Idle is okay, go to step 11).
10. Check throttle body, intake manifold, and EGR valve for vacuum leaks. If a problem is found, repair as necessary. Retest system. If no problem is found, go to next step.
11. Check for fuel contamination. If fuel is contaminated, repair as necessary. Retest system. If fuel is okay, go to next step.
12. Check PCM injector, power and sensor ground circuits for clean and tight connections. If a problem is found, repair as necessary. Retest system. If no problem is found, go to next step.
13. Disconnect MAF sensor harness connector. Operate vehicle in closed loop mode while monitoring scan tool BANK 1 S.T. FUEL TRIM. If S.T. FUEL TRIM does not decrease to about zero percent, go to next step. If S.T. FUEL TRIM decreases to about zero percent, go to step 19).
14. Perform FUEL SYSTEM PRESSURE TEST under BASIC FUEL SYSTEM CHECKS in appropriate BASIC TESTING article. If a problem is found, repair as necessary. Retest system. If no problem is found, go to next step.
15. Check intake manifold, injector "O" rings, EGR adapter, EGR valve and EGR feed pipes for vacuum leaks. If a problem is found, repair as necessary. Retest system. If no problem is found, go to next step.
16. Check exhaust system for corrosion, loose or missing hardware. If a problem is found, repair as necessary. Retest system. If no problem is found, go to next step.
17. Perform, INJECTOR BALANCE TEST. See FUEL SYSTEM in SYSTEM/COMPONENT TESTS article. If a problem is found, repair as necessary. Retest system. If no problem is found, go to next step.
18. Ensure HO2S is installed securely, and connector and harness are not contacting exhaust manifold or ignition wires. If a problem is found, repair as necessary. Retest system. If no problem is found, check for an intermittent problem, see DIAGNOSTIC AIDS .
19. Replace MAF sensor. Retest system.

Isuzu Trooper Limited 1997 - DTC P0175 - BANK 2 SYSTEM TOO RICH Diagnostic Aids

An intermittent may be caused by a poor connection, rubbed through wire insulation or a broken wire inside insulation. Inspect harness connectors for backed out terminals, improper mating, broken locks, improperly formed or damaged terminals, poor terminal-to-wire connection, and damaged harness. If DTC cannot be duplicated, check scan tool FAILURE RECORDS to determine mileage since last DTC was set.

1. Perform On-Board Diagnostic (OBD) System Check. Read and record FREEZE FRAME and/or FAIL RECORDS data for each DTC set. Go to next step.
2. If any DTCs other than P0172 and P0175 are set, diagnose them first before proceeding. If no other DTCs are set, go to next step.
3. Operate vehicle in closed loop mode while using scan tool to read BANK 1 L.T. FUEL TRIM values. If L.T. FUEL TRIM value is less than -15 percent for auto trans and is less than -12 percent for manual trans, go to step 5). If values are not as specified, go to next step.
4. Using scan tool, read and record FAIL RECORDS data. Clear DTCs and operate vehicle within FAILURE RECORDS conditions. If DTC P0175 is set, go to next step. If DTC P0175 is not set, check for an intermittent problem, see DIAGNOSTIC AIDS .
5. If DTC P0172 is also set, go to next step. If DTC P0172 is not set, go to step 15).
6. Check air filter element condition. Replace air filter element if necessary. Retest system. If air filter element is okay, go to next step.
7. Check for collapsed or restricted air intake duct. If a problem is found, repair as necessary. Retest system. If no problem is found, go to next step.
8. Check MAF inlet screen for blockage or foreign objects which may partially block airflow sample through MAF sensor. If a problem is found, repair as necessary. Retest system. If no problem is found, go to next step.
9. Start engine. If a high or unsteady idle condition exists, go to next step. If Idle is okay, go to step 11).
10. Turn ignition off. Check throttle body bore and throttle plate for restriction or foreign objects. Check for clogged IAC passages. If a problem is found, repair as necessary. Retest system. If no problem is found, go to next step.
11. Disconnect vacuum hose from fuel pressure regulator and check it for presence of fuel. If fuel is present, replace fuel pressure regulator. Retest system. If no fuel is present, go to next step.
12. Turn ignition on. Using scan tool, read TP ANGLE while slowly depressing accelerator pedal. If TP ANGLE increases steadily from zero percent at closed throttle to 100 percent at wide open throttle, go to next step. If TP ANGLE does not increase as specified, go to step 19).
13. Disconnect MAF sensor connector. Operate vehicle in closed loop mode while monitoring scan tool BANK 1 L.T. and BANK 1 S.T. FUEL TRIM. If both FUEL TRIM values decrease to about zero percent, go to step 20). If FUEL TRIM values do not decrease to about zero percent, go to next step.
14. Perform FUEL SYSTEM PRESSURE TEST. See BASIC TESTING article. If a problem is found, repair as necessary. Retest system. If no problem is found, go to next step.
15. Turn ignition on. Connect test light between canister purge solenoid connector terminals. If test light is on, go to next step. If test light is not on, replace PCM. Retest system.
16. Using an ohmmeter, check for continuity to ground in Red/Blue wire between PCM connector "A" terminal No. 15 and canister purge solenoid connector. See PIN VOLTAGE CHARTS. If continuity exists, repair short to ground. Retest system. If continuity to ground does not exist, go to next step.
17. Perform, INJECTOR BALANCE TEST. See FUEL SYSTEM in SYSTEM/COMPONENT TESTS article. If a problem is found, repair as necessary. Retest system. If no problem is found, go to next step.
18. Remove HO2S No. 1 and check for silicone contamination (powdery white deposit). If HO2S No. 1 is contaminated, replace HO2S No. 1. Retest system. If HO2S No. 1 is not contaminated, check for an intermittent problem, see DIAGNOSTIC AIDS .
19. Check for loose TP sensor mounting screws. Adjust TP sensor if necessary. If mounting screws are tight, replace TP sensor. Retest system.
20. Replace MAF sensor. Retest system.

Isuzu Trooper Limited 1997 - DTC P0201, P0202, P0203, P0204, P0205, P0206 - INJECTOR CIRCUIT NO. 1-6 Diagnostic Aids

An open or short in injector circuit will set DTC. The open or short will also cause a misfire and inoperative injector. A misfire DTC will be set indicating which cylinder is malfunctioning. Excessively high or low long and short term fuel trim indicate the possibility of a bad injector. Use INJECTOR COIL TEST in SYSTEM/COMPONENT TESTS article to check injector.

1. Perform On-Board (OBD) System Check. Read and record FREEZE FRAME and/or FAIL RECORDS data for each DTC set. Go to next step.
2. Attempt to start engine. If engine starts, go to next step. If engine does not start, see BASIC TESTING article.
3. Using scan tool, clear DTCs. Start and run engine for one minute and observe scan tool display. If any DTC from P0201 to P0206 resets, go to step 5). If no DTC resets, go to next step.
4. With ignition on and engine off, use scan tool to read FREEZE FRAME DATA and note parameters. Start engine and operate vehicle within FAILURE RECORDS conditions. If any DTC from P0201 to P0206 resets, go to next step. If no DTC resets, check for an intermittent problem, see DIAGNOSTIC AIDS .
5. Turn engine off. Disconnect affected injector harness connector related to DTC. Connect an injector tester (noid-light) to injector harness connector. Disable secondary ignition system to prevent engine from starting and crank engine. If noid-light blinks, go to INJECTOR COIL TEST in SYSTEM/COMPONENT TESTS article. If noid-light does not blink, go to next step.
6. If noid-light was on steady in previous step, go to next step. If noid-light did not come on in previous step, go to step 8).
7. Disconnect PCM connector containing affected injector circuit. Using a test light connected to battery positive terminal, probe affected injector driver circuit at harness connector. If test light comes on, repair short to ground in injector driver circuit. If test light does not come on, replace PCM. Retest system.
8. Disconnect injector harness connector. Using an ohmmeter connected to Red/Blue wire of injector harness connector, probe wire for affected cylinder. If ohmmeter shows continuity, go to next step. If ohmmeter shows no continuity, repair open in injector harness wire. Retest system.
9. At PCM side of injector harness connector, check for short to voltage in affected cylinder wire. If short to voltage exists, repair short in affected cylinder wire. Retest system. If short to voltage does not exist, go to next step.
10. Check for open circuit in affected cylinder wire between PCM and injector harness connector. Repair as necessary. If wires are all okay, replace PCM. Retest system.

Isuzu Trooper Limited 1997 - DTC P0300 - RANDOM MISFIRE DETECTED Diagnostic Aids

Scan tool message MISFIRE CUR. #1-6, is helpful is determining if only a single cylinder is affected by misfire. Check ignition coil for cracks or damage. Substitute a known good ignition coil. Numerous short trip drives (under 3 miles), may fuel foul spark plugs and set DTC. If DTC cannot be duplicated, check scan tool FAILURE RECORDS to determine mileage since last DTC was set.

1. Perform On-Board (OBD) System Check. Read and record FREEZE FRAME and/or FAIL RECORDS data for each DTC set. Go to next step.
2. Start engine and run at idle. Using scan tool, read and record FREEZE FRAME data. Operate vehicle within FAILURE RECORDS conditions. Read MISFIRE CUR # display for each cylinder. If MISFIRE CUR # increases (indicating an occurring misfire) for any cylinder, go to next step. If MISFIRE CUR # does not increase, check for an intermittent problem, see DIAGNOSTIC AIDS .
3. Check vacuum hoses for splits, kinks or improper connections. If a problem is found, repair as necessary. Retest system. If no problem is found, go to next step.
4. Check intake manifold, injector "O" rings, EGR valve and EGR feed pipes for vacuum leaks. If a problem is found, repair as necessary. Retest system. If no problem is found, go to next step.
5. Check PCV valve for improper installation or damaged hose. If a problem is found, repair as necessary. Retest system. If no problem is found, go to next step.
6. Inspect MAF inlet screen for foreign objects or damage that may block airflow to MAF sensor. Repair as necessary. Retest system. If inlet screen is okay, go to next step.
7. Remove EGR valve and inspect valve, seat and passages for damage. Inspect valve pintle to ensure it is not sticking partially open. If a problem is found, repair as necessary. Retest system. If no problem is found, go to next step.
8. Install a spark tester on spark plug wire at spark plug end for cylinder indicating a misfire. Crank engine and check for a strong Blue spark. Repeat procedure for each affected cylinder. If spark is okay on all cylinders, go to step 13). If spark is not okay at all cylinders, go to next step.
9. Remove ignition coil related to misfiring cylinder. Check ignition coil for cracks or carbon tracking. If a problem is found, replace damaged coil. Retest system. If no problem is found, go to next step.
10. Remove spark plug(s) associated with misfiring cylinder(s). Check spark plugs for excessive fouling. If spark plugs are excessively fouled, diagnose and repair mechanical engine problem. If spark plugs are not excessively fouled, go to next step.
11. Check spark plug insulators for cracks, carbon tracking or other damage. If a problem is found, replace faulty spark plug(s). Retest system. If no problem is found, go to next step.
12. Disconnect MAF sensor harness connector. Operate vehicle in closed loop. while monitoring BANK 1 L.T. FUEL TRIM and BANK 1 S.T. FUEL TRIM parameters on scan tool. If L.T. FUEL TRIM decreases to less than 20 percent and ST FUEL TRIM decreases to less than 50 percent, replace HEX ignition coil control module. If scan tool display is not as specified, replace ignition coil related to affected cylinder. Retest system.
13. Ensure PCM injector ground, power ground and sensor ground connections are clean and tight. Repair as necessary. Retest system. If connections are okay, go to next step.
14. Perform FUEL PUMP PRESSURE TEST see BASIC TESTING article. If a problem was found, repair as necessary. Retest system. If no problem was found, go to next step.
15. Check for fuel contamination. If fuel is contaminated, repair as necessary. Retest system. If fuel is okay, go to next step.
16. Perform INJECTOR BALANCE TEST. See FUEL SYSTEM in SYSTEM/COMPONENT TESTS article. If a problem is found, repair as necessary. Retest system. If no problem is found, go to next step.
17. Diagnose mechanical engine problems such as; faulty camshaft, leaking or sticking valves, weak valve springs, damaged piston rings, loose or worn rocker arms, incorrect valve timing, leaking head gasket or loose or broken motor mounts. If a problem is found, repair as necessary. Retest system. If no problems are found, go to next step.
18. Check for a transmission Torque Converter Clutch (TCC) problem. See appropriate repair information. Repair as necessary. If no problem is found, replace MAF sensor. Retest system.

Isuzu Trooper Limited 1997 - DTC P0301, P0302, P0303, P0304, P0305, P0306 - CYLINDER NO. 1-6 MISFIRE Diagnostic Aids

Test system grounds. Use INJECTOR COIL TEST in SYSTEM/COMPONENT TESTS article to check injector. Check spark plugs for cracked insulator, carbon tracking, incorrect gap and wear. Check ignition coil for cracks or damage. Substitute a known good ignition coil.

1. Perform On-Board Diagnostic (OBD) System Check. Read and record FREEZE FRAME and/or FAIL RECORDS data for each DTC set. Go to next step.
2. Start engine and run at idle. Using scan tool, read and record FREEZE FRAME data. Operate vehicle within FAILURE RECORDS conditions. Read MISFIRE CUR # display for appropriate cylinder. If MISFIRE CUR # increases (indicating an occurring misfire) for affected cylinder, go to step 4). If MISFIRE CUR. # does not increase, go to next step.
3. Monitor MISFIRE HIST. # while operating vehicle and attempting to duplicate conditions which caused DTC to set. If MISFIRE HIST. # increases, go to next step. If MISFIRE HIST. # does not increase, check for an intermittent problem, see DIAGNOSTIC AIDS .
4. Check vacuum hoses for splits, kinks or improper connections. Check intake manifold for vacuum leak. If a problem is found, repair as necessary. Retest system. If no problem is found, go to next step.
5. Install spark tester at affected cylinder spark plug wire. Crank engine. If a strong Blue spark is present, go to step 8). If no spark or weak spark is present, go to next step.
6. Remove ignition coil related to misfiring cylinder. Check ignition coil for cracks or carbon tracking. If a problem is found, replace damaged coil. Retest system. If no problem is found, go to next step.
7. Using an ohmmeter, measure primary coil resistance. Resistance should be 0.8-1.3 ohms. Replace ignition coil if resistance is not as specified. If coil is okay, replace ignition control module. Retest system.
8. Remove spark plug associated with misfiring cylinder. Check spark plug for excessive fouling. If spark plug is excessively fouled, diagnose and repair mechanical engine problem. If spark plug is not excessively fouled, go to next step.
9. Check spark plug insulator for cracks, carbon tracking or other damage. If a problem is found, replace faulty spark plug. Retest system. If no problem is found, go to next step.
10. Perform INJECTOR BALANCE TEST. See FUEL SYSTEM in SYSTEM/COMPONENT TESTS article. If a problem is found, repair as necessary. Retest system. If no problem is found, go to next step.
11. Inspect injector "O" rings for vacuum leaks. If a problem is found, repair as necessary. Retest system. If no problem is found, go to next step.
12. Diagnose mechanical engine problems such as: faulty camshaft, leaking or sticking valves, weak valve springs, damaged piston rings, loose or worn rocker arms, incorrect valve timing, leaking head gasket or loose or broken motor mounts. If a problem is found, repair as necessary. Retest system. If no problems are found, check for an intermittent problem, see DIAGNOSTIC AIDS .

Isuzu Trooper Limited 1997 - DTC P0325 - KNOCK FILTER MODULE

NOTE:

If an engine knock can be heard, repair engine mechanical problem before proceeding with circuit test.

Isuzu Trooper Limited 1997 - Diagnostic Aids

Check PCM and KNOCK SENSOR (KS) connections. Ensure KS harness is not routed to close to high voltage wires. If DTC cannot be duplicated, check scan tool FAILURE RECORDS to determine mileage since last DTC was set.

1. Perform On-Board Diagnostic (OBD) System Check. Read and record FREEZE FRAME and/or FAIL RECORDS data for each DTC set. Go to next step.
2. Operate vehicle under conditions to allow DTC to set. Using scan tool, monitor SPECIFIC DTC parameter until DTC P0325 test runs. If scan tool indicates DTC P0325, replace PCM. Retest system. If DTC P0325 is not set, go to next step.
3. With ignition on and engine off, review and record FAILURE RECORDS for DTC P0325. Operate vehicle within FAILURE RECORDS conditions. Using scan tool, monitor SPECIFIC DTC parameter until DTC P0325 test runs. If scan tool indicates DTC P0325, replace PCM. Retest system. If DTC P0325 is not set, check for an intermittent problem, see DIAGNOSTIC AIDS .

Isuzu Trooper Limited 1997 - DTC P0327 - KNOCK SENSOR (KS) CIRCUIT

NOTE:

If an engine knock can be heard, repair engine mechanical problem before proceeding with circuit test.

Isuzu Trooper Limited 1997 - Diagnostic Aids

If DTC cannot be duplicated, check scan tool FAILURE RECORDS to determine mileage since last DTC was set.

1. Perform On-Board Diagnostic (OBD) System Check. Read and record FREEZE FRAME and/or FAIL RECORDS data for each DTC set. Go to next step.
2. Operate vehicle under conditions to allow DTC to set. Using scan tool, monitor SPECIFIC DTC parameter until DTC P0327 test runs. If scan tool indicates DTC P0327, go to step 4). If DTC P0327 is not set, go to next step.
3. With ignition on and engine off, review and record FAILURE RECORDS for DTC P0327. Operate vehicle within FAILURE RECORDS conditions. Using scan tool, monitor SPECIFIC DTC parameter until DTC P0327 test runs. If scan tool indicates DTC P0327, go to next step. If DTC P0327 is not set, check for an intermittent problem, see DIAGNOSTIC AIDS .
4. Check for damaged terminal at KS harness connector. Repair as necessary. Retest system. If KS harness connector is okay, go to next step.
5. Using a test light connected to battery positive terminal, probe KS harness connector Black/Blue wire (PCM side). If test light comes on, go to next step. If test light does not come on, repair open ground circuit. Retest system.
6. Ensure ignition is off. Disconnect PCM harness connectors. Check KS signal circuit for poor connection at PCM. Repair as necessary. Retest system. If connections are okay, go to next step.
7. Using a DVOM, check KS signal circuit between PCM and KS connector for an open, short to voltage or short to ground. Repair as necessary. Retest system. If wire is okay, go to next step.
8. Reconnect KS harness connector. Using an ohmmeter, measure resistance of KS between signal circuit at PCM harness connector and engine block. If resistance is 100 k/ohms, go to next step. If resistance is not as specified, replace KS. Retest system.
9. Connect a voltmeter between ground and KS signal circuit at PCM harness connector. Set to AC volts. Measure voltage produced by KS while tapping on engine lift bracket. If an AC voltage is produced, replace PCM. If no voltage is produced, replace KS. Retest system.

Isuzu Trooper Limited 1997 - DTC P0336 - CRANKSHAFT POSITION (CKP) SENSOR 58X REFERENCE SIGNAL CIRCUIT Diagnostic Aids

An intermittent may be caused by a poor connection, rubbed through wire insulation or a broken wire inside insulation. Inspect harness connectors for backed out terminals, improper mating, broken locks, improperly formed or damaged terminals, poor terminal-to-wire connection, and damaged harness. Connect voltmeter 58X reference circuit and wiggle harness and connectors. A change in voltage will indicate area of problem. If DTC cannot be duplicated, check scan tool FAILURE RECORDS to determine mileage since last DTC was set.

1. Perform On-Board Diagnostic (OBD) System Check. Read and record FREEZE FRAME and/or FAIL RECORDS data for each DTC set. Go to next step.
2. Attempt to start engine. If engine starts and runs, go to next step. If engine does not start and run, see BASIC TESTING article.
3. Using scan tool, clear DTC P0336. Start engine and allow it to idle for one minute. Read DTCs. If DTC P0336 resets, go to next step. If DTC does not reset, check for an intermittent problem, see DIAGNOSTIC AIDS .
4. Disconnect PCM and CMP sensor harness connectors. Check for an open or short to ground in 58X reference circuit between CKP sensor connector and PCM harness connector. If a problem is found, repair as necessary. Retest system. If no problem is found, go to next step.
5. Reconnect PCM and CKP sensor harness connectors. Using a voltmeter, measure voltage on 58X reference circuit at PCM harness connector while cranking engine. If reading is about 2.5 volts, go tostep 7). If voltage is not as specified, go to next step.
6. Check for faulty connections at CKP sensor. If a faulty connection is found, repair as necessary. If connections are okay, replace CKP sensor. Retest system.
7. Check for faulty connections at PCM. If a faulty connection is found, repair as necessary. If connections are okay, replace PCM. Retest system.

Isuzu Trooper Limited 1997 - DTC P0337 - CRANKSHAFT POSITION (CKP) SENSOR CIRCUIT/LOW FREQUENCY Diagnostic Aids

An intermittent may be caused by a poor connection, rubbed through wire insulation or a broken wire inside insulation. Inspect harness connectors for backed out terminals, improper mating, broken locks, improperly formed or damaged terminals, poor terminal-to-wire connection, and damaged harness. Connect voltmeter 58X reference circuit and wiggle harness and connectors. A change in voltage will indicate area of problem. If DTC cannot be duplicated, check scan tool FAILURE RECORDS to determine mileage since last DTC was set.

1. Perform On-Board Diagnostic (OBD) System Check. Read and record FREEZE FRAME and/or FAIL RECORDS data for each DTC set. Go to next step.
2. Attempt to start engine. If engine starts and runs, go to next step. If engine does not start and run, see BASIC TESTING article.
3. Using scan tool, clear DTC P0337. Start engine and allow it to idle for one minute. Read DTCs. If DTC P0337 resets, go to next step. If DTC does not reset, check for an intermittent problem, see DIAGNOSTIC AIDS .
4. Turn ignition off and disconnect CKP sensor. Turn ignition on. Connect a voltmeter between 5-volt reference and sensor ground terminals at harness connector. If reading is 4-6 volts, go to step 7). If reading is not as specified, go to next step.
5. Using a voltmeter, backprobe between PCM harness connector 5-volt reference circuit and ground terminals. If reading is 4-6 volts, go to next step. If reading is not as specified, go to step 10).
6. Check CKP sensor 5-volt reference circuit and ground circuit between CKP sensor and PCM for an open, short to ground or short to power. Repair as necessary. Retest system.
7. Turn ignition off and disconnect PCM and CKP sensor harness connectors. Check for an open or short to ground in 58X reference circuit between CKP sensor connector and PCM harness connector. If a problem is found, repair as necessary. Retest system. If no problem is found, go to next step.
8. Reconnect PCM and CKP sensor harness connectors. Using a voltmeter, measure voltage of 58X reference circuit at PCM harness connector while cranking engine. If reading about 2.5 volts, go tostep 10). If reading is not as specified, go to next step.
9. Inspect connections at CKP sensor. Repair connections as necessary. If connections are okay, replace CKP sensor. Retest system.
10. Inspect connections at PCM. Repair connections as necessary. If connections are okay, replace PCM. Retest system.

Isuzu Trooper Limited 1997 - DTC P0341 - CAMSHAFT POSITION (CMP) SENSOR CIRCUIT PERFORMANCE Diagnostic Aids

An intermittent may be caused by a poor connection, rubbed through wire insulation or a broken wire inside insulation. Inspect harness connectors for backed out terminals, improper mating, broken locks, improperly formed or damaged terminals, poor terminal-to-wire connection, and damaged harness. Disconnect PCM connector. Connect voltmeter to CMP signal circuit and wiggle harness and connectors. A change in voltage will indicate area of problem. If DTC cannot be duplicated, check scan tool FAILURE RECORDS to determine mileage since last DTC was set.

1. Perform On-Board Diagnostic (OBD) System Check. Read and record FREEZE FRAME and/or FAIL RECORDS data for each DTC set. Go to next step.
2. Turn ignition on. Using scan tool, read and record FAIL RECORDS data for DTC P0341. Operate vehicle within FAILURE RECORDS conditions. Using scan tool, read SPECIFIC DTC. If scan tool displays DTC P0341 FAILED THIS IGN, go to next step. If scan tool does not display DTC P0341 FAILED THIS IGN, check for an intermittent problem, see DIAGNOSTIC AIDS .
3. Disconnect CMP sensor. Using a voltmeter, measure voltage between sensor ground circuit and senor voltage reference circuit at CMP sensor harness connector. If reading is 4-6 volts, go to next step. If reading is not as specified, go to step 5).
4. Measure voltage between CMP sensor signal circuit and sensor ground circuit at CMP sensor harness connector. If reading is 4-6 volts, go to step 11). If reading is not as specified, go to step 8).
5. If voltage measured in step 3) was less than 4-6 volts, go to next step. If voltage in step 3) was greater than 4-6 volts, repair short to power in CMP sensor voltage reference circuit. Retest system.
6. Inspect CMP sensor for poor connections. If a problem is found, repair as necessary. Retest system. If no problem is found, go to next step.
7. Turn ignition off. Disconnect PCM and CMP sensor harness connectors. Inspect sensor voltage reference circuits for an open between ignition control module and CMP sensor. If a problem is found, repair as necessary. Retest system. If no problem is found, go to step 9).
8. Turn ignition off. Disconnect PCM harness connectors and leave CMP sensor disconnected. Turn ignition on. Using a DVOM, check CMP sensor signal circuit for an open or short to power. Check CMP sensor input circuit for a short to ground. If a problem is found, repair as necessary. Retest system. If no problem is found, go to next step.
9. Check for an open or short in CMP sensor ground circuit. If a problem is found, repair as necessary. Retest system. If no problem is found, go to next step.
10. Check for poor connection at PCM. If a problem is found, repair as necessary. Retest system. If no problem is found, go to next step.
11. Reconnect PCM and CMP sensor harness connectors. Using a voltmeter, backprobe sensor connector at CMP signal circuit. Crank engine and monitor voltage. If voltage toggles between zero and 4 volts, replace PCM. Retest system. If voltage is not as specified, leave voltmeter connected and go to next step.
12. Leaving sensor wiring harness connected, remove CMP sensor. Place a magnet on CMP senor large enough to cover face of sensor. Observe voltmeter. If reading is about zero volts, replace faulty or missing sensor magnet. If reading is not as specified, replace CMP sensor. Retest system.

Isuzu Trooper Limited 1997 - DTC P0342 - CAMSHAFT POSITION (CMP) SENSOR CIRCUIT LOW Diagnostic Aids

An intermittent may be caused by a poor connection, rubbed through wire insulation or a broken wire inside insulation. Inspect harness connectors for backed out terminals, improper mating, broken locks, improperly formed or damaged terminals, poor terminal-to-wire connection, and damaged harness. Disconnect PCM connector. Connect voltmeter to CMP signal circuit and wiggle harness and connectors. A change in voltage will indicate area of problem. If DTC cannot be duplicated, check scan tool FAILURE RECORDS to determine mileage since last DTC was set.

1. Perform On-Board Diagnostic (OBD) System Check. Read and record FREEZE FRAME and/or FAIL RECORDS data for each DTC set. Go to next step.
2. Turn ignition on. Using scan tool, read and record FAIL RECORDS data for DTC P0342. Operate vehicle within FAILURE RECORDS conditions. Using scan tool, read SPECIFIC DTC. If scan tool displays DTC P0342 FAILED THIS IGN, go to next step. If scan tool does not display DTC P0342 FAILED THIS IGN, check for an intermittent problem, see DIAGNOSTIC AIDS .
3. Disconnect CMP sensor. Turn ignition on. Using a voltmeter, measure voltage at CMP sensor harness connector between sensor voltage reference circuit and sensor ground circuit. If reading is 4-6 volts, go to step 7). If reading is not as specified, go to next.
4. Turn ignition off. Disconnect PCM and CMP sensor harness connectors. Check for poor connections at CMP sensor. If a problem is found, repair as necessary. Retest system. If no problem is found, go to next step.
5. Check for poor connection at PCM. If a problem is found, repair as necessary. Retest system. If no problem is found, go to next step.
6. Inspect CMP sensor voltage reference circuit for an open or short to ground. Inspect CMP sensor ground circuit for an open or short to power. Repair as necessary. Retest system.
7. With ignition on and engine off, measure voltage between CMP sensor signal circuit and sensor ground circuit at CMP sensor harness connector. If reading is about 4-6 volts, got to next step. If reading is not as specified, go to step 9).
8. Turn ignition off. Disconnect PCM harness connectors. Turn ignition on. Connect a voltmeter between ground and CMP sensor signal circuit at PCM harness connector. Monitor voltage while repeatedly touching CMP sensor signal circuit at CMP sensor connection with a test light to ground. If voltmeter displays voltage toggling between zero and 5 volts when test light is touched to CMP sensor signal circuit, leave voltmeter connected and go to step 12). If voltage is not as specified, go to next step.
9. Leaving PCM disconnected, turn ignition on. Probe CMP sensor signal circuit at PCM harness connector with a test light connected to battery positive terminal. If test light comes on, locate and repair short at ground in CMP signal circuit. Retest system. If test light does not come on, go to next step.
10. Probe CMP sensor signal circuit with a test light connected to ground. If test light comes on, locate and repair short to voltage in CMP sensor signal circuit. Retest system. If test light does not come on, go to next step.
11. Turn ignition off. Disconnect CMP sensor harness connector. Using an ohmmeter, check CMP sensor signal circuit for an open. If problem is found, repair as necessary. Retest system.
12. Remove CMP sensor and reconnect harness connector. Place a magnet on CMP senor large enough to cover face of sensor. Observe voltmeter. If reading is about zero volts, go to next step. If reading is not as specified, replace CMP sensor. Retest system.
13. Reinstall CMP sensor, leaving voltmeter connected. Crank engine and observe voltmeter. If reading toggles between zero and 4 volts, replace PCM. If reading is not as specified, replace faulty or missing CMP sensor magnet. Retest system.

Isuzu Trooper Limited 1997 - DTC P0351, P0352, P0353, P0354, P0355, P0356 - IGNITION CIRCUIT NO. 1-6 Diagnostic Aids

An intermittent may be caused by a poor connection, rubbed through wire insulation or a broken wire inside insulation. Inspect harness connectors for backed out terminals, improper mating, broken locks, improperly formed or damaged terminals, poor terminal-to-wire connection, and damaged harness. Using scan tool, monitor DTC P0351-P0356 and wiggle harness and connectors. A change in voltage will indicate area of problem. If DTC cannot be duplicated, check scan tool FAILURE RECORDS to determine mileage since last DTC was set.

1. Perform On-Board Diagnostic (OBD) System Check. Read and record FREEZE FRAME and/or FAIL RECORDS data for each DTC set. Go to next step.
2. Turn ignition on. Using scan tool, read and record FAIL RECORDS data for DTCs P0351-P0356. Operate vehicle within FAILURE RECORDS conditions. Using scan tool, read SPECIFIC DTC. If scan tool displays a DTC between DTC P0351 and DTC P0356, go to next step. If scan tool does not display any DTC, check for an intermittent problem, see DIAGNOSTIC AIDS .
3. Check ignition control module for poor connection or damaged terminals. If a problem is found, repair as necessary. Retest system. If no problem is found, go to next step.
4. Check PCM harness connector for poor connection or damaged terminals. If a problem is found, repair as necessary. Retest system. If no problem is found, go to next step.
5. Turn ignition on. Using a voltmeter, backprobe between ground and affected ignition control circuit at PCM harness connector. If reading is 25-55 mV, go to next step. If reading is not as specified, go to step 8).
6. Start engine and let idle. Using voltmeter, backprobe between ground and ignition control circuit at PCM harness connector for cylinder being tested. If reading toggles between 100 and 180 mV, go to next step. If reading is not as specified, replace PCM. Retest system.
7. Turn ignition off. Disconnect 3-pin and 5-pin connectors at ignition control module. Using a voltmeter, measure voltage of affected ignition control circuit at ignition control module while cranking engine. If reading is 200-1200 mV, replace ignition control module. If reading is not as specified, repair open in affected ignition control circuit. Retest system.
8. Turn ignition off. Disconnect PCM and ignition control module harness connectors. Using an ohmmeter, check affected ignition control circuit for a short to ground. Repair as necessary. If circuit is okay, go to next step.
9. Turn ignition on. Using a voltmeter, check affected ignition control circuit for a short to voltage. Repair as necessary. If circuit is okay, replace PCM. Retest system.

Isuzu Trooper Limited 1997 - DTC P0401 - EGR FLOW INSUFFICIENT Diagnostic Aids

An intermittent may be caused by a poor connection, rubbed through wire insulation or a broken wire inside insulation. Inspect harness connectors for backed out terminals, improper mating, broken locks, improperly formed or damaged terminals, poor terminal-to-wire connection, and damaged harness. Using scan tool, monitor ACTUAL EGR POSITION and wiggle harness and connectors. A change in voltage will indicate area of problem. If DTC cannot be duplicated, check scan tool FAILURE RECORDS to determine mileage since last DTC was set.

1. Perform On-Board Diagnostic (OBD) System Check. Read and record FREEZE FRAME and/or FAIL RECORDS data for each DTC set. Go to next step.
2. If DTC P1406 is also set, go to DTC P1406. If DTC P1406 is not set, go to next step.
3. Start engine. Using scan tool, monitor MAP signal. Quickly press throttle half way down and release. If scan tool value made an immediate large change, replace MAP sensor. If scan tool value is not as specified, go to next step.
4. Inspect exhaust system for modifications or leaks. If a problem is found, repair as necessary and go to step 7). If no problem is found, go to next step.
5. Remove EGR valve and check pintle, valve and passages and adapter for excessive deposits or restriction. Check EGR valve gasket and pipes for leaks. If a problem is found, repair as necessary and go to step 7). If no problem is found, go to next step.
6. Remove EGR inlet and outlet pipes from exhaust and intake manifolds. Inspect manifold EGR ports and pipes for blockage. If a problem is found, repair as necessary and go to next step. If no problem is found, check for an intermittent problem, see DIAGNOSTIC AIDS .
7. Read and record FAIL RECORDS data for DTC P0401. Clear DTCs. Start engine and monitor system info screen while moving connectors and wiring harnesses related to EGR valve. If scan tool displays DTC P0401 FAILED THIS IGN, go to last step completed in this DTC test. If scan tool does not display DTC P0401 FAILED THIS IGN, repair is complete.

Isuzu Trooper Limited 1997 - DTC P0420, P0430 - LOW CATALYST EFFICIENCY BANK 1 AND 2 (AUTO TRANS) Diagnostic Aids

An intermittent may be caused by a poor connection, rubbed through wire insulation or a broken wire inside insulation. Inspect harness connectors for backed out terminals, improper mating, broken locks, improperly formed or damaged terminals, poor terminal-to-wire connection, and damaged harness. If DTC cannot be duplicated, check scan tool FAILURE RECORDS to determine mileage since last DTC was set.

1. Perform On-Board Diagnostic (OBD) System Check. Read and record FREEZE FRAME and/or FAIL RECORDS data for each DTC set. Go to next step.
2. Diagnose any other DTCs before proceeding. If no other DTCs are set, go to next step.
3. Ensure TWC is an original equipment part. Check TWC for dents or discoloration caused by excessive heat. Ensure rattle caused by internal catalyst damage does not exist. If a problem is found, repair as necessary and go to step 6). If no problems are found, go to next step.
4. Check exhaust system for leaks, damage, loose or missing hardware. If a problem is found, repair as necessary and go to step 7). If no problems are found, go to next step.
5. Ensure HO2S No. 2, bank 2 is securely installed and that harness is not damaged or contacting exhaust system. If a problem is found, repair as necessary and go to step 7). If no problems are found, go to next step.
6. Replace affected TWC. Check for possible engine misfire DTC or engine mechanical problem, and go to next step.
7. Read and record FAIL RECORDS data for DTC P0420 or DTC P0430. Clear DTCs. Start engine and allow coolant temperature to reach 140?F (60?C). Run engine while monitoring scan tool IAC RPM control function to maintain MAF sensor range at 8-50 grams per second for at least 2 minutes. Go to next step.
8. Using scan tool, monitor TWC MONITOR TEST COUNTER while operating vehicle within conditions required to set DTC. Continue operating vehicle until TWC MONITOR TEST COUNTER reaches 49 and returns to zero at least 2 times. Read SPECIFIC DTC. If scan tool displays DTC P0420 or DTC P0430 TEST RAN AND PASSED, repair is complete. If scan tool does not display DTC P0420 or DTC P0430 TEST RAN AND PASSED, return to step 2).

Isuzu Trooper Limited 1997 - DTC P0420, P0430 - LOW CATALYST EFFICIENCY BANK 1 AND 2 (MAN. TRANS) Diagnostic Aids

An intermittent may be caused by a poor connection, rubbed through wire insulation or a broken wire inside insulation. Inspect harness connectors for backed out terminals, improper mating, broken locks, improperly formed or damaged terminals, poor terminal-to-wire connection, and damaged harness. If DTC cannot be duplicated, check scan tool FAILURE RECORDS to determine mileage since last DTC was set.

1. Perform On-Board Diagnostic (OBD) System Check. Read and record FREEZE FRAME and/or FAIL RECORDS data for each DTC set. Go to next step.
2. Diagnose any other DTCs before proceeding. If no other DTCs are set, go to next step.
3. Ensure TWC is an original equipment part. Check TWC for dents or discoloration caused by excessive heat. Ensure rattle caused by internal catalyst damage does not exist. If a problem is found, repair as necessary and go to step 6). If no problems are found, go to next step.
4. Check exhaust system for leaks, damage, loose or missing hardware. If a problem is found, repair as necessary and go to step 7). If no problems are found, go to next step.
5. Ensure HO2S No. 3, bank 1 is securely installed and that harness is not damaged or contacting exhaust system. If a problem is found, repair as necessary and go to step 7). If no problems are found, go to next step.
6. Replace affected TWC. Check for possible engine misfire DTC or engine mechanical problem, and go to next step.
7. Read and record FAIL RECORDS data for DTC P0420 or DTC P0430. Clear DTCs. Start engine and allow coolant temperature to reach 140?F (60?C). Run engine while monitoring scan tool IAC RPM control function to maintain MAF sensor range at 8-50 grams per second for at least 2 minutes. Go to next step.
8. Using scan tool, monitor TWC MONITOR TEST COUNTER while operating vehicle within conditions required to set DTC. Continue operating vehicle until TWC MONITOR TEST COUNTER reaches 49 and returns to zero at least 2 times. Read SPECIFIC DTC. If scan tool displays DTC P0420 or DTC P0430 TEST RAN AND PASSED, repair is complete. If scan tool does not display DTC P0420 or DTC P0430 TEST RAN AND PASSED, return to step 2).

Isuzu Trooper Limited 1997 - DTC P0440 - EVAP SYSTEM Diagnostic Aids

An intermittent may be caused by a cracked or punctured EVAP canister, damaged or disconnected vacuum, vent or purge line. Check for poor connection, rubbed through wire insulation or a broken wire inside insulation. Inspect harness connectors for backed out terminals, improper mating, broken locks, improperly formed or damaged terminals, poor terminal-to-wire connection, and damaged harness. If DTC cannot be duplicated, check scan tool FAILURE RECORDS to determine mileage since last DTC was set.

1. Perform On-Board Diagnostic (OBD) System Check. Read and record FREEZE FRAME and/or FAIL RECORDS data for each DTC set. Go to next step.
2. If DTC P1655 or P1675 is set, diagnose affected DTCs before proceeding. If DTCs are not set, go to next step.
3. Turn ignition off. Remove fuel cap. Turn ignition on. Using scan tool, read FUEL TANK PRESSURE. If scan tool displays zero in. H2O, go to next step. If scan tool does not display zero in. H2O, repair faulty fuel tank pressure sensor circuit.
4. Zero pressure and vacuum gauges on EVAP Pressure/Purge Cart (J41413). Reinstall fuel cap. Read and record FAIL RECORDS data for DTC P0440. Clear DTCs. Using scan tool, command EVAP vent solenoid ON (closed). Connect EVAP pressure/purge cart to EVAP service port. Using EVAP pressure/purge cart, attempt to pressurize EVAP system to 5 in. H2O. If specified pressure is not achieved, to step 6). If specified pressure is achieved, go to next step.
5. Maintain EVAP system pressure at 5 in. H2O. Using scan tool, read FUEL TANK PRESSURE. If scan tool displays -5 in. H2O, go to step 8). If scan tool does not display -5 in. H2O, go to step 7).
6. Disconnect fuel tank vapor and EVAP purge lines from EVAP canister. Plug fuel tank vapor line fitting at EVAP canister. Connect a hand vacuum pump to EVAP purge line fitting at EVAP canister. Ensure EVAP vent solenoid is still commanded ON (closed). Attempt to apply 5 in. Hg vacuum to EVAP canister. If vacuum is maintained as specified, go to step 11). If vacuum can not be maintained as specified, go to step 10).
7. Check fuel tank vapor line and EVAP purge line for restriction. If restriction is found, repair as necessary and go to step 16). If no restriction is found, repair faulty fuel tank pressure sensor circuit.
8. Disconnect vacuum source line and plug vacuum source fitting at EVAP purge solenoid. Using scan tool, select and activate SYSTEM PERF. Using EVAP pressure/purge cart, pressurize EVAP system to 5 in. H2O. Observe pressure gauge on EVAP pressure/purge cart while removing plug from vacuum source fitting line at EVAP purge solenoid. If fuel tank vacuum decreases to zero in. H2O within 15 seconds, go to step 9). If vacuum does not decrease as specified, go to step 13).
9. Connect EVAP pressure/purge cart vacuum gauge to vacuum source line. Start engine. Run engine speed to greater than 2000 RPM while observing vacuum gauge. If vacuum is greater than 15 in. Hg, check for an intermittent problem, see DIAGNOSTIC AIDS . If vacuum is 15 in. Hg or less, go to step 14).
10. Check if vent hose is disconnected or damaged. Check EVAP canister for damage. If a problem is found, repair as necessary and go to step 16). If no problem is found, go to step 15).
11. Check for missing or faulty fuel cap. Check for disconnected or leaking fuel tank vapor line. Check for disconnected or damaged EVAP purge line. If a problem is found, repair as necessary and go to step 16). If no problem is found, go to next step.
12. Using scan tool, command EVAP vent solenoid ON (closed). With EVAP pressure/purge cart connected to EVAP service port, continuously attempt to pressurize EVAP system by leaving EVAP pressure/purge cart control knob in PRESSURIZE position. Using Ultrasonic Leak Detector (J41416), locate and repair EVAP system leak. It may be necessary to lower fuel tank to check connections at top of tank. Go to step 16).
13. Replace EVAP purge solenoid and go to step 16).
14. Locate and repair cause of no source vacuum to EVAP purge solenoid and go to step 16).
15. Replace EVAP vent solenoid and go to next step.
16. Turn ignition on, engine off. Using scan tool, command EVAP vent solenoid ON (closed). Using EVAP pressure/purge cart pressurize EVAP system to 15 in. H2O. Monitor EVAP pressure/purge cart pressure gauge. Turn EVAP pressure/purge cart rotary switch to HOLD position. If pressure decreases to less than 10 in H2O within 2 minutes, return to step 3). If pressure does not decrease as specified, repair is complete.

Isuzu Trooper Limited 1997 - DTC P0442 - EVAP SYSTEM SMALL LEAK DETECTED Diagnostic Aids

An intermittent may be caused by a cracked or punctured EVAP canister, damaged or disconnected vacuum, vent or purge line. Check for poor connection, rubbed through wire insulation or a broken wire inside insulation. Inspect harness connectors for backed out terminals, improper mating, broken locks, improperly formed or damaged terminals, poor terminal-to-wire connection, and damaged harness. If DTC cannot be duplicated, check scan tool FAILURE RECORDS to determine mileage since last DTC was set.

1. Perform On-Board Diagnostic (OBD) System Check. Read and record FREEZE FRAME and/or FAIL RECORDS data for each DTC set. Go to next step.
2. If DTC P1655 or P1675 is set, diagnose affected DTC(s) before proceeding. If DTCs are not set, go to next step.
3. Turn ignition off. Remove fuel cap. Turn ignition on. Using scan tool, read FUEL TANK PRESSURE. If scan tool displays zero in. H2O go to next step. If scan tool does not display zero in. H2O, repair faulty fuel tank pressure sensor circuit.
4. Zero pressure and vacuum gauges on EVAP Pressure/Purge Cart (J41413). Reinstall fuel cap. Read and record FAIL RECORDS data for DTC P0442. Clear DTCs. Connect EVAP pressure/purge cart to EVAP service port. Using scan tool, command EVAP vent solenoid ON (closed). Using EVAP pressure/purge cart, pressurize EVAP system to 5 in. H2O. If specified pressure is achieved, go to next step. If specified pressure is not achieved, repair faulty fuel tank pressure sensor circuit.
5. Start engine and allow to idle. Using scan tool, command EVAP vent solenoid ON (closed). Using EVAP pressure/purge cart pressurize EVAP system to 15 in. H2O. Monitor EVAP pressure/purge cart pressure gauge. Turn EVAP pressure/purge cart rotary switch to HOLD position. If pressure decreases to less than 10 in. H2O within 2 minutes, go to next step. If pressure does not decrease as specified, check for an intermittent problem, see DIAGNOSTIC AIDS .
6. Disconnect fuel tank vapor and EVAP purge lines from EVAP canister. Plug fuel tank vapor line fitting at EVAP canister. Connect a hand vacuum pump to EVAP purge line fitting at EVAP canister. Ensure EVAP vent solenoid is still commanded ON (closed). Attempt to apply 5 in. Hg vacuum to EVAP canister. If vacuum is maintained as specified, go to step 9). If vacuum can not be maintained as specified, go to next step.
7. Check if vent hose is disconnected or damaged. Check EVAP canister for damage. If a problem is found, repair as necessary and go to step 11). If no problem is found, go to next step.
8. Replace EVAP vent solenoid and go to step 11).
9. Check for missing or faulty fuel cap. Check for disconnected or leaking fuel tank vapor line. Check for disconnected or damaged EVAP purge line. If a problem is found, repair as necessary and go to step 11. If no problem is found, go to next step.
10. Using scan tool, command EVAP vent solenoid on (closed). With EVAP pressure/purge cart connected to EVAP service port, attempt to pressurize EVAP system by leaving EVAP pressure/purge cart control knob in PRESSURIZE position. Using Ultrasonic Leak Detector (J41416), locate and repair EVAP system leak. It may be necessary to lower fuel tank to check connections at top of tank. Go to next step.
11. Turn ignition on, engine off. Using scan tool, command EVAP vent solenoid on (closed). Using EVAP pressure/purge cart pressurize EVAP system to 15 in. H2O. Monitor EVAP pressure/purge cart pressure gauge. Turn EVAP pressure/purge cart rotary switch to HOLD position. If pressure decreases to less than 10 in. H2O within 2 minutes, return to step 3). If pressure does not decrease as specified, repair is complete.

Isuzu Trooper Limited 1997 - DTC P0446 - EVAP CANISTER VENT BLOCKED Diagnostic Aids

An intermittent may be caused by a damaged, restricted or disconnected vacuum, vent or purge line. Check for poor connection, rubbed through wire insulation or a broken wire inside insulation. Inspect harness connectors for backed out terminals, improper mating, broken locks, improperly formed or damaged terminals, poor terminal-to-wire connection, and damaged harness. If DTC cannot be duplicated, check scan tool FAILURE RECORDS to determine mileage since last DTC was set.

1. Perform On-Board Diagnostic (OBD) System Check. Read and record FREEZE FRAME and/or FAIL RECORDS data for each DTC set. Go to next step.
2. If DTC P1675 is also set, diagnose DTC P1675 before proceeding. If DTC is not set, go to next step.
3. Turn ignition on. Read and record FAIL RECORDS data for DTC P0446. Clear DTCs. Turn ignition off. Remove fuel cap. Turn ignition on. Using scan tool, read FUEL TANK PRESSURE. If scan tool displays zero in. H20, go to next step. If scan tool does not display zero in. H2O, repair faulty fuel tank sensor circuit.
4. Zero pressure and vacuum gauges on EVAP Pressure/Purge Cart (J41413). Reinstall fuel cap. Using scan tool, command EVAP vent solenoid ON (closed). Connect EVAP pressure/purge cart to EVAP service port. Using EVAP pressure/purge cart, pressurize EVAP system to 5 in. H2O. Using scan tool, read FUEL TANK PRESSURE. If scan tool displays 5 in. H2O, go to next step. If scan tool does not display 5 in. H2O, repair faulty fuel tank pressure sensor circuit.
5. Maintain EVAP system pressure at 5 in. H2O. Using scan tool, command EVAP vent solenoid OFF (open). Monitor EVAP pressure/purge cart pressure gauge. If pressure decreases to zero in. H2O within 5 seconds, check for an intermittent problem, see DIAGNOSTIC AIDS . If pressure does not decrease as specified, go to next step.
6. Disconnect vent hose, marked "AIR", from EVAP canister. Switch EVAP pressure/purge cart rotary switch to PURGE. Start engine and allow it to reach operating temperature. Monitor vacuum gauge for 5 seconds while holding engine speed at 2500 RPM. If vacuum remains at less than 30 in. H2O, go to next step. If vacuum does not remain as specified, go to step 9).
7. Check if vent hose is between EVAP canister and EVAP solenoid is kinked, pinched or blocked. If a problem is found, repair as necessary and go to step 10). If no problem is found, go to next step.
8. Replace EVAP vent solenoid and go to step 10).
9. Replace EVAP canister and go to next step.
10. Using scan tool, command EVAP vent solenoid ON (closed). With EVAP pressure/purge cart connected to EVAP service port, pressurize EVAP system to 5 in. H2O. Switch EVAP pressure/purge cart rotary switch to HOLD. Using scan tool, command EVAP vent solenoid OFF (open). If pressure decreases to zero in. H2O within 5 seconds, repair is complete. If pressure does not decrease as specified, return to step 3).

Isuzu Trooper Limited 1997 - DTC P0461 - FUEL LEVEL SENSOR CIRCUIT PERFORMANCE Diagnostic Aids

Check for poor connection, rubbed through wire insulation or a broken wire inside insulation. Inspect harness connectors for backed out terminals, improper mating, broken locks, improperly formed or damaged terminals, poor terminal-to-wire connection, and damaged harness. Using scan tool monitor fuel level display while moving connectors and harness related to fuel sensor. Change in display will indicate problem area.

1. Perform On-Board Diagnostic (OBD) System Check. Read and record FREEZE FRAME and/or FAIL RECORDS data for each DTC set. Go to next step.
2. If a Vehicle Speed Sensor (VSS) DTC is also set, diagnose it before proceeding. If a VSS DTC is not set, go to next step.
3. Remove fuel level sensor from fuel tank. Ensure sensor arm moves freely. If sensor arm does not move freely, replace fuel level sensor. Retest system. If fuel level sensor is okay, go to next step.
4. Connect an analog ohmmeter to fuel level sensor. As arm of sensor is moved, needle on meter should move smoothly. Replace fuel level sensor if operation is not as specified. Retest system. If operation is as specified, go to next step.
5. Using an ohmmeter, measure resistance of fuel level sensor as arm is moved from empty to full positions. Ensure resistance is within specification. See FUEL LEVEL SENSOR SPECIFICATIONS . Replace fuel level sensor if operation is not as specified. If fuel level sensor tests okay, replace PCM. Retest system.
   

   Isuzu Trooper Limited 1997 FUEL LEVEL SENSOR SPECIFICATIONS
   

   Position	Ohms
   "E"	102.5-120.5
   1/6	73
   1/3	56
   1/2	45
   2/3	36.75
   5/6	30
   "F"	17-23.5

Isuzu Trooper Limited 1997 - DTC P0462 - FUEL LEVEL SENSOR CIRCUIT LOW VOLTAGE Diagnostic Aids

Check for poor connection, rubbed through wire insulation or a broken wire inside insulation. Inspect harness connectors for backed out terminals, improper mating, broken locks, improperly formed or damaged terminals, poor terminal-to-wire connection, and damaged harness. Using scan tool monitor fuel level display while moving connectors and harness related to fuel sensor. Change in display will indicate problem area.

1. Perform On-Board Diagnostic (OBD) System Check. Read and record FREEZE FRAME and/or FAIL RECORDS data for each DTC set. Go to next step.
2. If any Engine Coolant Temperature (ECT) or Manifold Absolute Pressure (MAP) sensor DTCs are set, diagnose them first. If no other DTCs are set, go to next step.
3. Disconnect fuel level sensor harness connector. Turn ignition on. Using a voltmeter, measure voltage between sensor harness positive and ground wires. If reading is 5 volts, go to step 8). If reading is not as specified, go to next step.
4. Using a voltmeter, backprobe between ground and PCM harness connector terminal which supplies 5 volts to fuel level sensor. If reading is 5 volts, go to next step. If reading is not as specified, replace PCM. Retest system.
5. Backprobe between ground and 5-volt reference circuit at sensor. If reading is about same as in step 4), go to step 7). If reading is not as specified, go to next step.
6. Check for an open or high resistance in 5-volt reference circuit between PCM and fuel level sensor. Repair as necessary. Retest system.
7. Check for an open or high resistance in ground circuit between PCM and fuel level sensor. Repair as necessary. Retest system.
8. Remove fuel level sensor from fuel tank. Ensure sensor arm moves freely. Using an ohmmeter, measure resistance of fuel level sensor as arm is moved from empty to full positions. Ensure resistance is within specification. See FUEL LEVEL SENSOR SPECIFICATIONS . Replace fuel level sensor if operation is not as specified. If fuel level sensor tests okay, replace PCM. Retest system.

Isuzu Trooper Limited 1997 - DTC P0463 - FUEL LEVEL SENSOR CIRCUIT HIGH VOLTAGE Diagnostic Aids

Check for poor connection, rubbed through wire insulation or a broken wire inside insulation. Inspect harness connectors for backed out terminals, improper mating, broken locks, improperly formed or damaged terminals, poor terminal-to-wire connection, and damaged harness. Using scan tool monitor fuel level display while moving connectors and harness related to fuel sensor. Change in display will indicate problem area.

1. Perform On-Board Diagnostic (OBD) System Check. Read and record FREEZE FRAME and/or FAIL RECORDS data for each DTC set. Go to next step.
2. If any Engine Coolant Temperature (ECT) or Manifold Absolute Pressure (MAP) sensor DTCs are set, diagnose them first. If no other DTCs are set, go to next step.
3. Disconnect fuel level sensor harness connector. Turn ignition on. Using a voltmeter, measure voltage between sensor harness positive and ground wires. If reading is 5 volts, go to step 8). If reading is not as specified, go to next step.
4. Turn ignition off. Reconnect fuel level sensor harness connector. Turn ignition on. Using a voltmeter, connect negative lead to ground. Backprobe positive lead to sensor ground circuit at harness connector. If voltmeter indicates a short to voltage source, go to next step. If no short is detected, go to step 6).
5. Repair short to voltage between fuel level sensor and PCM. Retest system.
6. With negative lead still connected to ground, backprobe 5-volt reference sensor circuit at harness connector. If reading is greater than 5 volts, repair circuit for short to power. If reading is not as specified, go to next step.
7. Check 5-volt reference circuit for short to ground. Repair as necessary. If no short is found, replace PCM. Retest system.
8. Turn ignition off. Remove fuel level sensor from fuel tank. Ensure sensor arm moves freely. Using an ohmmeter, measure resistance of fuel level sensor as arm is moved from empty to full positions. Ensure resistance is within specification. See FUEL LEVEL SENSOR SPECIFICATIONS . Replace fuel level sensor if operation is not as specified. If fuel level sensor tests okay, replace PCM. Retest system.

Isuzu Trooper Limited 1997 - DTC P0502 - VEHICLE SPEED SENSOR (VSS) CIRCUIT/LOW INPUT

1. Perform On-Board Diagnostic (OBD) System Check. Read and record FREEZE FRAME and/or FAIL RECORDS data for each DTC set. Go to next step.
2. Check speedometer. If speedometer works, go to step 10). If speedometer does not work, go to next step.
3. Disconnect VSS harness connector and turn ignition on (with engine off). Connect a test light to positive battery terminal. Probe VSS connector ground terminal. If test light illuminates, go to step 5). If test light does not illuminate, go to next step.
4. Repair sensor ground. Retest system.
5. With sensor disconnected, turn ignition on. Using DVOM, probe VSS connectors ground and voltage supply. If battery voltage is not displayed on DVOM, go to next step. If battery voltage is displayed, go to step 7).
6. Repair open or short to ground. After repair ensure meter fuse is not blown. Retest system.
7. With sensor disconnected, turn ignition on. Using DVOM, measure voltage between VSS connector ground and speedometer wire. If DVOM reads 7.5-8.0 volts, go to step 9). If reading is not as specified, go to next step.
8. Repair open or short circuit between speedometer and VSS. Retest system.
9. Replace speedometer. Retest system.
10. Turn ignition off. Disconnect MAF sensor connector. Remove air cleaner assembly. Disconnect 16-pin connector, located behind left headlight assembly. Connect jumper wire between battery voltage and transmission side of 16-pin connector Blue/Yellow wire. Using DVOM, measure voltage between ground and 16-pin connector Light Green wire. Disconnect Blue connector located next to 16-pin connector. Connect jumper wire between VSS ground at Blue connector Black/Red wire and ground. Raise and support rear of vehicle. Place transmission in Neutral. Rotating rear wheels by hand, observe DVOM readings. If reading toggles between .6 volt and 10 volts, go to step 12). If readings are not as specified, go to next step.
11. Replace VSS. Retest system.
12. Repair open or short between PCM and speedometer. Retest system. If problem was not found, go to next step.
13. Replace PCM. Retest system.

Isuzu Trooper Limited 1997 - DTC P0506 - IDLE CONTROL SYSTEM LOW RPM Diagnostic Aids

Check for poor connection, rubbed through wire insulation or a broken wire inside insulation at PCM and IAC motor. Inspect harness connectors for backed out terminals, improper mating, broken locks, improperly formed or damaged terminals, poor terminal-to-wire connection, and damaged harness. Ensure air intake system is not restricted. Check throttle body for blockage and carbon build up. Clean as necessary. Inspect for a large vacuum leak at brake booster or PCV. If DTC cannot be duplicated, check scan tool FAILURE RECORDS to determine mileage since last DTC was set.

1. Perform On-Board Diagnostic (OBD) System Check. Read and record FREEZE FRAME and/or FAIL RECORDS data for each DTC set. Go to next step.
2. Using scan tool, read DTCs. If any other DTCs are set, diagnose them first before proceeding. If no other DTCs are set, go to next step.
3. Start engine. Turn all accessories off. Using scan tool, monitor ENGINE SPEED and command engine speed up to 1500 RPM, down to 500 RPM, then back up to 1500 RPM. If ENGINE SPEED remains within 50 RPM of desired RPM for each command, check for an intermittent problem, see DIAGNOSTIC AIDS . If operation is not as specified, go to next step.
4. Disconnect IAC harness connector. Install IAC Noid-Light (J37027A) in IAC harness connector. With engine running, monitor noid-lights while commanding engine speed up to 1500 RPM, down to 500 RPM, then back up to 1500 RPM. Both noid-lights should cycle Green and Red, but not OFF as RPM changes from 500-1500 RPM. If noid-lights flash as specified, go to step 6). If noid-lights do not flash as specified, go to next step.
5. Check IAC "A" high and low and "B" high and low circuits for an open, short to voltage, short to ground or poor connection at PCM. If a problem is found, repair as necessary. Retest system. If no problem is found, go to step 9).
6. Ensure throttle stop screw has not been tampered with. Check for stuck IAC valve or throttle linkage. Check for restrictions, collapse or blockage in air intake system. Check throttle body bore and IAC valve for excessive deposits. If a problem is found, repair as necessary. Retest system. If no problem is found, go to next step.
7. Check for faulty connection at IAC valve harness connector. If faulty connection is found, repair as necessary. Retest system. If connection is okay, go to next step.
8. Replace IAC valve. Retest system.
9. Replace PCM. Retest system.

Isuzu Trooper Limited 1997 - DTC P0507 - IDLE CONTROL SYSTEM HIGH RPM Diagnostic Aids

Check for poor connection, rubbed through wire insulation or a broken wire inside insulation at PCM and IAC motor. Inspect harness connectors for backed out terminals, improper mating, broken locks, improperly formed or damaged terminals, poor terminal-to-wire connection, and damaged harness. Ensure air intake system is not restricted. Check throttle body for blockage and carbon build up. Clean as necessary. Check for vacuum leak. If DTC cannot be duplicated, check scan tool FAILURE RECORDS to determine mileage since last DTC was set.

1. Perform On-Board Diagnostic (OBD) System Check. Read and record FREEZE FRAME and/or FAIL RECORDS data for each DTC set. Go to next step.
2. Using scan tool, read DTCs. If any other DTCs are set, diagnose them first before proceeding. If no other DTCs are set, go to next step.
3. Start engine. Turn all accessories off. Using scan tool, monitor ENGINE SPEED and command engine speed up to 1500 RPM, down to 500 RPM, then back up to 1500 RPM. If ENGINE SPEED remains within 50 RPM of desired RPM for each command, check for an intermittent problem, see DIAGNOSTIC AIDS . If operation is not as specified, go to next step.
4. Disconnect IAC harness connector. Install IAC Noid-Light (J37027A ) in IAC harness connector. With engine running, monitor noid-lights while commanding engine speed up to 1500 RPM, down to 500 RPM, then back up to 1500 RPM. Both noid-lights should cycle Green and Red, but not OFF as RPM changes from 500-1500 RPM. If noid-lights flash as specified, go to step 6). If noid-lights do not flash as specified, go to next step.
5. Check IAC "A" high and low and "B" high and low circuits for an open, short to voltage or short to ground. If a problem is found, repair as necessary. Retest system. If no problem is found, go to step 9).
6. Ensure throttle stop screw has not been tampered with. Check for stuck IAC valve or throttle linkage. Check for correct PCV valve installation. Ensure no vacuum leaks are present. If a problem is found, repair as necessary. Retest system. If no problem is found, go to next step.
7. Check for faulty connection at IAC valve harness connector. If faulty connection is found, repair as necessary. Retest system. If connection is okay, go to next step.
8. Replace IAC valve. Retest system.
9. Replace PCM. Retest system.

Isuzu Trooper Limited 1997 - DTC P0562 - SYSTEM LOW VOLTAGE Diagnostic Aids

If DTC sets when an accessory is operated, check component for poor connection or excessive draw.

1. Perform On-Board Diagnostic (OBD) System Check. Read and record FREEZE FRAME and/or FAIL RECORDS data for each DTC set. Go to next step.
2. Using DVOM, measure voltage at battery. If reading is greater than 11.5 volts, go to next step. If reading is 11.5 volts or less, charge battery before proceeding to next step.
3. Install scan tool and select IGNITION VOLTS. Place vehicle in Neutral or Park. Start engine, raise engine speed to 2000 RPM and load electrical system (turn on headlights, blower, radio, etc.). If scan tool reads 12.8-14.1 volts, go to next step. If reading is not as specified, see ALTERNATOR & REGULATOR article.
4. Turn ignition off. Disconnect PCM harness connector. Turn ignition on, engine off. Using a DVOM, measure ignition voltage at PCM terminal A4 (Red/White wire). If output is equal to battery voltage, check for excessive current draw with ignition off. If voltage is not equal to battery voltage, go to next step.
5. Check for poor connections at PCM harness terminals. Repair as necessary. Retest system. If no problem is found, go to next step.
6. Check for an open ignition feed circuit to PCM. Repair as necessary. Retest system. If no problem is found, go to next step.
7. Replace PCM. Retest system.

Isuzu Trooper Limited 1997 - DTC P0563 - SYSTEM HIGH VOLTAGE Diagnostic Aids

If DTC sets when an accessory is operated, check component for poor connection or excessive draw.

1. Perform On-Board Diagnostic (OBD) System Check. Read and record FREEZE FRAME and/or FAIL RECORDS data for each DTC set. Go to next step.
2. Using DVOM, measure voltage at battery. If reading is less than 11.5 volts, go to next step. If reading is 11.5 volts or more, go to step 4).
3. Charge battery and clean terminals and cable connections. If voltage is less than 11.5 volts, replace battery. If voltage is 11.5 volts or more, go next step.
4. Turn all accessories off. Install scan tool and select ignition voltage parameter. Place vehicle in Park or Neutral. Start engine and increase engine speed to 2000 RPM. If scan tool reading is more than 2.5 volts greater than voltage measured in step 2) or 3), see ALTERNATOR & REGULATOR article. If voltage is not as specified, go to next step.
5. Check for excessive current draw with ignition off. If excessive current draw present, see DIAGNOSTIC AIDS . If no excessive current draw is present, go to next step.
6. Replace PCM. Retest system.

Isuzu Trooper Limited 1997 - DTC P0601 - PCM MEMORY ERROR

1. Perform On-Board Diagnostic (OBD) System Check. Read and record FREEZE FRAME and/or FAIL RECORDS data for each DTC set. Go to next step.
2. Replace PCM. After repair is completed, repeat OBD system check.

Isuzu Trooper Limited 1997 - DTC P1106 - MAP SENSOR CIRCUIT INTERMITTENT HIGH VOLTAGE Diagnostic Aids

Inspect MAP sensor line for leakage or being plugged. Check for poor connection, rubbed through wire insulation or a broken wire inside insulation at PCM and IAC motor. Inspect harness connectors for backed out terminals, improper mating, broken locks, improperly formed or damaged terminals, poor terminal-to-wire connection, and damaged harness. Check for vacuum leak. If DTC cannot be duplicated, check scan tool FAILURE RECORDS to determine mileage since last DTC was set.

1. Perform On-Board Diagnostic (OBD) System Check. Read and record FREEZE FRAME and/or FAIL RECORDS data for each DTC set. Go to next step.
2. Using scan tool, select LAST TEST FAIL. Record any other failed DTCs. If DTC P0108 is also set, diagnose DTC P0108 before proceeding. If DTC is not set, go to next step.
3. If DTC P1111, P1115, and/or P1121 is also set, go to step 6). If none of these DTCs are set, go to next step.
4. Check for faulty sensor ground circuit terminal at MAP sensor. If problem is found, go to step 9). If no problem is found, go to next step.
5. Check MAP signal circuit between MAP sensor harness connector and PCM for intermittent short to voltage. If a problem is found, go to step 10). If no problem is found, go to step 8).
6. Check for intermittent short to voltage on 5-volt reference circuit between PCM and MAP, EGR, "G" and TP sensors. If a problem is found, go to step 10). If no problem is found, go to next step.
7. Check for faulty ground circuit terminal connection at PCM. If problem is found, go to step 9). If no problem is found, go to next step.
8. Check for intermittent open or faulty splice in sensor ground circuit. If a problem is found, go to step 10). If no problem is found, check for an intermittent problem, see DIAGNOSTIC AIDS .
9. Replace faulty connector terminal. Retest system.
10. Locate and repair intermittent open/short circuit. Retest system.

Isuzu Trooper Limited 1997 - DTC P1107 - MAP SENSOR CIRCUIT INTERMITTENT LOW VOLTAGE Diagnostic Aids

Check for poor connection, rubbed through wire insulation or a broken wire inside insulation at PCM and IAC motor. Inspect harness connectors for backed out terminals, improper mating, broken locks, improperly formed or damaged terminals, poor terminal-to-wire connection, and damaged harness. Check for vacuum leak. If DTC cannot be duplicated, check scan tool FAILURE RECORDS to determine mileage since last DTC was set.

1. Perform On-Board Diagnostic (OBD) System Check. Read and record FREEZE FRAME and/or FAIL RECORDS data for each DTC set. Go to next step.
2. Using scan tool, select LAST TEST FAIL. Record any other failed DTCs. If DTC P0107 is also set, diagnose DTC P0107 before proceeding. If DTC is not set, go to next step.
3. If DTC P1122 is also set, go to step 6). If DTC is not set, go to next step.
4. Check for faulty 5-volt reference or signal circuit connection at MAP sensor. If a problem is found, go to step 9). If no problem is found, go to next step.
5. Check signal circuit between MAP sensor and PCM for intermittent open or short to ground. If problem is found, go to step 10). If no problem is found, go to step 8).
6. Check for intermittent short to ground on 5-volt reference circuit between PCM and EGR valve, MAP, "G" and TP sensors. If a problem is found, go to step 10). If no problem is found, go to next step.
7. Check for faulty 5-volt reference circuit connection at PCM. If faulty connection is found, go to step 9). If connection is okay, go to next step.
8. Check for intermittent open or faulty splice in 5-volt reference circuit. If a problem is found, go to step 10). If no problem is found, check for an intermittent problem, see DIAGNOSTIC AIDS .
9. Replace faulty connector terminal(s). Retest system.
10. Repair circuit as necessary. Retest system.

Isuzu Trooper Limited 1997 - DTC P1111 - IAT SENSOR CIRCUIT INTERMITTENT HIGH VOLTAGE Diagnostic Aids

Check for poor connection, rubbed through wire insulation or a broken wire inside insulation at PCM and IAC motor. Inspect harness connectors for backed out terminals, improper mating, broken locks, improperly formed or damaged terminals, poor terminal-to-wire connection, and damaged harness. Check for vacuum leak. If DTC cannot be duplicated, check scan tool FAILURE RECORDS to determine mileage since last DTC was set.

1. Perform On-Board Diagnostic (OBD) System Check. Read and record FREEZE FRAME and/or FAIL RECORDS data for each DTC set. Go to next step.
2. Using scan tool, select LAST TEST FAIL. Record any other failed DTCs. If DTC P0113 is also set, diagnose DTC P0113 before proceeding. If DTC is not set, go to next step.
3. If DTC P1106, P1115, and/or P1121 is also set, go to step 6). If none of these DTCs are set, go to next step.
4. Check for faulty sensor ground circuit terminal at IAT sensor. If problem is found, repair as necessary. Retest system. If no problem is found, go to next step.
5. Check for faulty signal circuit connection at IAT sensor. If faulty connection is found, repair as necessary. Retest system. If connection is okay, go to next step.
6. Check IAT signal circuit between IAT sensor harness connector and PCM for intermittent open. If open is found, repair as necessary. Retest system. If no open is found, go to next step.
7. Check IAT signal circuit between IAT sensor harness connector and PCM for intermittent short to voltage. If short to voltage is found, repair as necessary. Retest system. If no short to voltage is found, go to next step.
8. Check for faulty ground circuit terminal connection at PCM. If problem is found, repair as necessary. Retest system. If no problem is found, go to next step.
9. Check for intermittent open or faulty splice in sensor ground circuit. If a problem is found, repair as necessary. Retest system. If no problem is found, check for an intermittent problem, see DIAGNOSTIC AIDS .

Isuzu Trooper Limited 1997 - DTC P1112 - IAT SENSOR CIRCUIT INTERMITTENT LOW VOLTAGE Diagnostic Aids

Check for poor connection, rubbed through wire insulation or a broken wire inside insulation at PCM and IAC motor. Inspect harness connectors for backed out terminals, improper mating, broken locks, improperly formed or damaged terminals, poor terminal-to-wire connection, and damaged harness. Check for vacuum leak. If DTC cannot be duplicated, check scan tool FAILURE RECORDS to determine mileage since last DTC was set.

1. Perform On-Board Diagnostic (OBD) System Check. Read and record FREEZE FRAME and/or FAIL RECORDS data for each DTC set. Go to next step.
2. If DTC P0112 is also set, diagnose DTC P0112 before proceeding. If DTC is not set, go to next step.
3. Check IAT signal circuit between IAT sensor harness connector and PCM for intermittent short to ground. If short to ground is found, repair as necessary. Retest system. If no short to ground is found, check for an intermittent problem, see DIAGNOSTIC AIDS .

Isuzu Trooper Limited 1997 - DTC P1114 - ECT SENSOR CIRCUIT INTERMITTENT LOW VOLTAGE Diagnostic Aids

Check for poor connection, rubbed through wire insulation or a broken wire inside insulation at PCM and IAC motor. Inspect harness connectors for backed out terminals, improper mating, broken locks, improperly formed or damaged terminals, poor terminal-to-wire connection, and damaged harness. Check for vacuum leak. If DTC cannot be duplicated, check scan tool FAILURE RECORDS to determine mileage since last DTC was set.

1. Perform On-Board Diagnostic (OBD) System Check. Read and record FREEZE FRAME and/or FAIL RECORDS data for each DTC set. Go to next step.
2. If DTC P0117 is also set, diagnose DTC P0117 before proceeding. If DTC is not set, go to next step.
3. Check ECT signal circuit between ECT sensor harness connector and PCM for intermittent short to ground. If short to ground is found, repair as necessary. Retest system. If no short to ground is found, check for an intermittent problem, see DIAGNOSTIC AIDS .

Isuzu Trooper Limited 1997 - DTC P1115 - ECT SENSOR CIRCUIT INTERMITTENT HIGH VOLTAGE Diagnostic Aids

Check for poor connection, rubbed through wire insulation or a broken wire inside insulation at PCM and IAC motor. Inspect harness connectors for backed out terminals, improper mating, broken locks, improperly formed or damaged terminals, poor terminal-to-wire connection, and damaged harness. Check for vacuum leak. If DTC cannot be duplicated, check scan tool FAILURE RECORDS to determine mileage since last DTC was set.

1. Perform On-Board Diagnostic (OBD) System Check. Read and record FREEZE FRAME and/or FAIL RECORDS data for each DTC set. Go to next step.
2. If DTC P0118 is also set, diagnose DTC P0118 before proceeding. If DTC is not set, go to next step.
3. If DTC P1106, P1111, and/or P1121 is also set, go to step 8). If none of these DTCs are set, go to next step.
4. Check for faulty sensor ground circuit terminal at ECT sensor. If problem is found, repair as necessary. Retest system. If no problem is found, go to next step.
5. Check for faulty signal circuit connection at ECT sensor. If faulty connection is found, repair as necessary. Retest system. If connection is okay, go to next step.
6. Check ECT signal circuit between ECT sensor harness connector and PCM for intermittent open. If open is found, repair as necessary. Retest system. If no open is found, go to next step.
7. Check ECT signal circuit between ECT sensor harness connector and PCM for intermittent short to voltage. If short to voltage is found, repair as necessary. Retest system. If no short to voltage is found, go to next step.
8. Check for faulty ground circuit terminal connection at PCM. If problem is found, repair as necessary. Retest system. If no problem is found, go to next step.
9. Check for intermittent open or faulty splice in sensor ground circuit. If a problem is found, repair as necessary. Retest system. If no problem is found, check for an intermittent problem, see DIAGNOSTIC AIDS .

Isuzu Trooper Limited 1997 - DTC P1121 - TP SENSOR CIRCUIT INTERMITTENT HIGH VOLTAGE Diagnostic Aids

Check for poor connection, rubbed through wire insulation or a broken wire inside insulation at PCM and IAC motor. Inspect harness connectors for backed out terminals, improper mating, broken locks, improperly formed or damaged terminals, poor terminal-to-wire connection, and damaged harness. Check for vacuum leak. If DTC cannot be duplicated, check scan tool FAILURE RECORDS to determine mileage since last DTC was set.

1. Perform On-Board Diagnostic (OBD) System Check. Read and record FREEZE FRAME and/or FAIL RECORDS data for each DTC set. Go to next step.
2. If DTC P0123 is also set, diagnose DTC P0123 before proceeding. If DTC is not set, go to next step.
3. If DTC P1106, P1111, and/or P1115 is also set, go to step 6). If none of these DTCs are set, go to next step.
4. Check for faulty sensor ground circuit terminal at TP sensor. If problem is found, go to step 9). If no problem is found, go to next step.
5. Check TP signal circuit between TP sensor harness connector and PCM for intermittent short to voltage. If a problem is found, go tostep 10). If no problem is found, go to step 8).
6. Check for intermittent short to voltage on 5-volt reference circuit between PCM and MAP, EGR and TP sensors. If a problem is found, go to step 10). If no problem is found, go to next step.
7. Check for faulty ground circuit terminal connection at PCM. If problem is found, go to step 9). If no problem is found, go to next step.
8. Check for intermittent open or faulty splice in sensor ground circuit. If a problem is found, go to step 10). If no problem is found, check for an intermittent problem, see DIAGNOSTIC AIDS .
9. Replace faulty connector terminal. Retest system.
10. Locate and repair intermittent open/short circuit. Retest system.

Isuzu Trooper Limited 1997 - DTC P1122 - TP SENSOR CIRCUIT INTERMITTENT LOW VOLTAGE Diagnostic Aids

Check for poor connection, rubbed through wire insulation or a broken wire inside insulation at PCM and IAC motor. Inspect harness connectors for backed out terminals, improper mating, broken locks, improperly formed or damaged terminals, poor terminal-to-wire connection, and damaged harness. Check for vacuum leak. If DTC cannot be duplicated, check scan tool FAILURE RECORDS to determine mileage since last DTC was set.

1. Perform On-Board Diagnostic (OBD) System Check. Read and record FREEZE FRAME and/or FAIL RECORDS data for each DTC set. Go to next step.
2. If DTC P0122 is also set, diagnose DTC P0122 before proceeding. If DTC is not set, go to next step.
3. If DTC P1107 is also set, go to step 6). If DTC is not set, go to next step.
4. Check for faulty 5-volt reference or signal circuit connection at TP sensor. If a problem is found, go to step 9). If no problem is found, go to next step.
5. Check signal circuit between TP sensor and PCM for intermittent open or short to ground. If problem is found, go to step 10). If no problem is found, go to step 8).
6. Check for intermittent short to ground on 5-volt reference circuit between PCM and EGR valve, MAP and TP sensors. If a problem is found, go to step 10). If no problem is found, go to next step.
7. Check for faulty 5-volt reference circuit connection at PCM. If faulty connection is found, go to step 9). If connection is okay, go to next step.
8. Check for intermittent open or faulty splice in 5-volt reference circuit. If a problem is found, go to step 10). If no problem is found, check for an intermittent problem, see DIAGNOSTIC AIDS.
9. Replace faulty connector terminal(s). Retest system.
10. Repair circuit as necessary. Retest system.

Isuzu Trooper Limited 1997 - DTC P1133 - HEATED OXYGEN SENSOR (HO2S) NO. 1 BANK 1 CIRCUIT/INSUFFICIENT SWITCHING Diagnostic Aids

An intermittent problem can be caused by misrouted harness, rubbed-through wire insulation or broken wire inside insulation of HO2S heater circuit. If connections and wiring are okay and DTC continues to reset, replace HO2S 1. Check scan tool FAILURE RECORDS to determine mileage since last DTC was set.

1. Perform On-Board Diagnostic (OBD) System Check. Read and record FREEZE FRAME and/or FAIL RECORDS data for each DTC set. Go to next step.
2. If any DTC other than P1153 or P1154 sets, diagnose affected DTC before proceeding. If no other DTC sets, start engine and allow it to idle. Operate vehicle within conditions required to set DTC. Using scan tool, read SPECIFIC DTC. If scan tool displays DTC P1133 FAILED THIS IGN, go to next step. If scan tool does not display DTC P1133 FAILED THIS IGN, check for an intermittent problem, see DIAGNOSTIC AIDS .
3. If DTC P1153 or P1154 is also set, go to step 11). If DTC is not set, go to next step.
4. Check exhaust system for leaks. If exhaust leak is found, repair as necessary and go to step 2). If no exhaust leak is found, go to next step.
5. Visually inspect HO2S No. 1 for secure installation or corrosion on terminals. Check terminal tension at HO2S No. 1 and PCM. Check for damaged wiring. If a problem is found, repair as necessary. Retest system. If no problem is found, go to next step.
6. Disconnect HO2S No. 1 connector. Connect a DVOM to PCM side of connectors high signal and ground, and low signal and ground. Turn ignition on and read DVOM at each connection. If reading is 3-4 millivolts, go to step 9). If voltage is not as specified, go to next step.
7. Turn ignition off and check for damage to PCM pins or terminals. If a problem was found repair as necessary. Retest system. If no problem was found, go to next step.
8. Inspect signal circuit for a short to voltage, ground or an open. If problem was found repair as necessary. Retest system. If no problem was found, go to next step.
9. With ignition off, disconnect PCM connector. Disconnect HO2S No. 1 and check for high and low signal circuits, located between PCM and HO2S No. 1 for shorting together. If a problem was found, repair as necessary. Retest system. If no problem was found, go to next step.
10. Connect PCM and disconnected Bank 1 HO2S No. 1. Using scan tool, check voltage. If reading is 425-475 millivolts, go to step 12), If voltage is not as specified, got step 13).
11. Check for fuel contamination, use of improper RTV sealant or engine oil and coolant consumption. Replace affected HO2S. Retest system.
12. Replace HO2S 1. Retest system.
13. Replace PCM. Retest system.

Isuzu Trooper Limited 1997 - DTC P1134 - HEATED OXYGEN SENSOR (HO2S) NO. 1 BANK 1 CIRCUIT TRANSITION TIME RATIO Diagnostic Aids

An intermittent problem can be caused by misrouted harness, rubbed-through wire insulation or broken wire inside insulation of HO2S heater circuit. If connections and wiring are okay and DTC continues to reset, replace HO2S 1. Check scan tool FAILURE RECORDS to determine mileage since last DTC was set.

1. Perform On-Board Diagnostic (OBD) System Check. Read and record FREEZE FRAME and/or FAIL RECORDS data for each DTC set. Go to next step.
2. If any DTC other than P1153 or P1154 sets, diagnose affected DTC before proceeding. If no other DTC sets, start engine and allow it to idle. Operate vehicle within conditions required to set DTC. Using scan tool, read SPECIFIC DTC. If scan tool displays DTC P1134 FAILED THIS IGN, go to next step. If scan tool does not display DTC P1134 FAILED THIS IGN, check for an intermittent problem, see DIAGNOSTIC AIDS .
3. If DTC P1153 and/or P1154 is also set, go to step 11). If DTC is not set, go to next step.
4. Check exhaust system for leaks. If exhaust leak is found, repair as necessary. Retest system. If no exhaust leak is found, go to next step.
5. Visually inspect HO2S No. 1 for secure installation or corrosion on terminals. Check terminal tension at HO2S No. 1 and PCM. Check for damaged wiring. If a problem is found, go to step 8). If no problem is found, go to next step.
6. Disconnect HO2S No. 1 connector. Turn ignition on. Using DVOM, probe connector, measure voltage between high signal circuit and ground, and low signal circuit and ground. If DVOM reads 3-4 volts, go to next step. If voltage is not as specified, go to step 9).
7. Turn ignition off. With HO2S No. 1 disconnected, connect a jumper wire between HO2S No. 1 harness connector high signal, low signal circuits and ground. Turn ignition on. If scan tool reading jump from .01 volt to .45 volt when jumper is removed, go to step 11). If voltage does not change as specified, go to step 12).
8. Repair condition as necessary. Retest system.
9. Check for poor PCM connections or terminal damage. Repair as necessary. Retest system. If no problem is found, go to next step.
10. Repair open, grounded or shorted signal circuit. Retest system. If no problem is found, go to step 7).
11. Remove Bank 1 HO2S No. 1 and check it for fuel contamination, improper RTV sealant (white powdery coating on sensor) and engine oil or coolant consumption. Repair as necessary. Retest system. If no problem is found, go to step 13).
12. Replace PCM. Retest system.
13. Replace HO2S No. 1. Retest system.

Isuzu Trooper Limited 1997 - DTC P1153 - HEATED OXYGEN SENSOR (HO2S) NO. 1 BANK 2 CIRCUIT/INSUFFICIENT SWITCHING Diagnostic Aids

An intermittent problem can be caused by misrouted harness, rubbed-through wire insulation or broken wire inside insulation of HO2S heater circuit. If connections and wiring are okay and DTC continues to reset, replace HO2S 1. Check scan tool FAILURE RECORDS to determine mileage since last DTC was set.

1. Perform On-Board Diagnostic (OBD) System Check. Read and record FREEZE FRAME and/or FAIL RECORDS data for each DTC set. Go to next step.
2. If any DTC other than P1133 or P1134 sets, diagnose affected DTC before proceeding. If no other DTC sets, start engine and allow it to idle. Operate vehicle within conditions required to set DTC. Using scan tool, read SPECIFIC DTC. If scan tool displays DTC P1153 FAILED THIS IGN, go to next step. If scan tool does not display DTC P1153 FAILED THIS IGN, check for an intermittent problem, see DIAGNOSTIC AIDS .
3. If DTC P1133 or P1134 is also set, go to step 11). If DTC is not set, go to next step.
4. Check exhaust system for leaks. If exhaust leak is found, repair as necessary and go to step 2). If no exhaust leak is found, go to next step.
5. Visually inspect HO2S No. 1 for secure installation or corrosion on terminals. Check terminal tension at HO2S No. 1 and PCM. Check for damaged wiring. If a problem is found, repair as necessary. Retest system. If no problem is found, go to next step.
6. Disconnect HO2S No. 1 connector. Connect a DVOM to PCM side of connectors high signal and ground, and low signal and ground. Turn ignition on and read DVOM at each connection. If reading is 3-4 millivolts, go to step 9). If voltage is not as specified, go to next step.
7. Turn ignition off and check for damage to PCM pins or terminals. If a problem was found repair as necessary. Retest system. If no problem was found, go to next step.
8. Inspect signal circuit for a short to voltage, ground or an open. If problem was found repair as necessary. Retest system. If no problem was found, go to next step.
9. With ignition off, disconnect PCM connector. Disconnect HO2S No. 1 and check for high and low signal circuits, located between PCM and HO2S No. 1 for shorting together. If a problem was found, repair as necessary. Retest system. If no problem was found, go to next step.
10. Connect PCM and disconnected Bank 2 HO2S No. 1. Using scan tool, check voltage. If reading is 425-475 millivolts, go to step 12), If voltage is not as specified, got step 13).
11. Check for fuel contamination, use of improper RTV sealant or engine oil and coolant consumption. Replace affected HO2S. Retest system.
12. Replace HO2S 1. Retest system.
13. Replace PCM. Retest system.

Isuzu Trooper Limited 1997 - DTC P1154 - HEATED OXYGEN SENSOR (HO2S) NO. 1 BANK 2 CIRCUIT TRANSITION TIME RATIO Diagnostic Aids

An intermittent problem can be caused by misrouted harness, rubbed-through wire insulation or broken wire inside insulation of HO2S heater circuit. If connections and wiring are okay and DTC continues to reset, replace HO2S 1. Check scan tool FAILURE RECORDS to determine mileage since last DTC was set.

1. Perform On-Board Diagnostic (OBD) System Check. Read and record FREEZE FRAME and/or FAIL RECORDS data for each DTC set. Go to next step.
2. If any DTC other than P1133 or P1134 sets, diagnose affected DTC before proceeding. If no other DTC sets, start engine and allow it to idle. Operate vehicle within conditions required to set DTC. Using scan tool, read SPECIFIC DTC. If scan tool displays DTC P1154 FAILED THIS IGN, go to next step. If scan tool does not display DTC P1154 FAILED THIS IGN, check for an intermittent problem, see DIAGNOSTIC AIDS .
3. If DTC P1133 and/or P1134 is also set, go to step 11). If DTC is not set, go to next step.
4. Check exhaust system for leaks. If exhaust leak is found, repair as necessary. Retest system. If no exhaust leak is found, go to next step.
5. Visually inspect HO2S No. 1 for secure installation or corrosion on terminals. Check terminal tension at HO2S No. 1 and PCM. Check for damaged wiring. If a problem is found, go to step 8). If no problem is found, go to next step.
6. Disconnect HO2S No. 1 connector. Turn ignition on. Using DVOM, probe connector, measure voltage between high signal circuit and ground, and low signal circuit and ground. If DVOM reads 3-4 volts, go to next step. If voltage is not as specified, go to step 9).
7. Turn ignition off. With HO2S No. 1 disconnected, connect a jumper wire between HO2S No. 1 harness connector high signal, low signal circuits and ground. Turn ignition on. If scan tool reading jump from .01 volt to .45 volt when jumper is removed, go to step 11). If voltage does not change as specified, go to step 12).
8. Repair condition as necessary. Retest system.
9. Check for poor PCM connections or terminal damage. Repair as necessary. Retest system. If no problem is found, go to next step.
10. Repair open, grounded or shorted signal circuit. Retest system. If no problem is found, go to step 7).
11. Remove Bank 2 HO2S No. 1 and check it for fuel contamination, improper RTV sealant (white powdery coating on sensor) and engine oil or coolant consumption. Repair as necessary. Retest system. If no problem is found, go to step 13).
12. Replace PCM. Retest system.
13. Replace HO2S No. 1. Retest system.

Isuzu Trooper Limited 1997 - DTC P1171 - FUEL SYSTEM LEAN DURING ACCELERATION Diagnostic Aids

A restricted fuel system may provide adequate fuel supply at idle, but not during acceleration. Water or alcohol in fuel may cause low HO2S voltage during acceleration. Check for defective or plugged fuel injectors. Check for low fuel.

1. Perform On-Board Diagnostic (OBD) System Check. Read and record FREEZE FRAME and/or FAIL RECORDS data for each DTC set. Go to next step.
2. If any other component-related DTCs are set, diagnose them first. If no other DTC is present, go to next step.
3. Check fuel level. Add fuel if tank is almost empty. If fuel was added, go to next step. If no additional fuel was required, go to step 5).
4. Start vehicle and bring engine to normal operating temperature, 167-203?F (75-95?C). Raise engine speed to 1200 RPM and using scan tool observe HO2S No. 1 voltage. If scan tool reading toggle between .1 and .9 volt and voltage raise to high end of specification when throttle is opened half way for a few seconds, see INJECTOR BALANCE TEST in SYSTEM/COMPONENT TESTS article. If voltage is not as specified, go to next step.
5. Turn ignition off. Relieve fuel pressure and install fuel pressure gauge. Start engine, bring to normal operating temperature and allow it to idle. Disconnect vacuum line to fuel pressure regulator and read pressure gauge. If pressure is 41-47 psi (280-325 kPa), see OBD II SYSTEM CHECK in BASIC TESTING article. If pressure reading is not as specified, go to next step.
6. Check for restricted fuel lines or filter. If problem is found, repair as necessary. Retest system. If no problem is found, go to next step.
7. Turn ignition off. Remove fuel pump relay. Using a fused jumper between battery terminal and fuel pump fuse terminals. With fuel pressure gauge still connected, pinch off fuel return line, not allowing fuel pressure to exceed 60 psi (412 kPa). Manipulate fuel line to raise pressure greater than 47 psi (325 kPa). If pressure rises greater than 47 psi (325 kPa), check for an intermittent problem, see DIAGNOSTIC AIDS . If pressure does not rise to 47 psi (325 kPa), go to next step.
8. Check for faulty fuel pump, restricted fuel pump strainer, incorrect fuel pump, incorrect fuel grade or hot fuel. If any problem is found, repair as necessary. Retest system.

Isuzu Trooper Limited 1997 - DTC P1390 - "G" SENSOR CIRCUIT INTERMITTENT LOW VOLTAGE Diagnostic Aids

An intermittent problem can be caused by misrouted harness, rubbed-through wire insulation or broken wire inside insulation. If connections and wiring appear okay, monitor scan tool "G" sensor display while moving sensor connections and related harnesses. Change in scan tool display will indicate area of fault. MAP and "G" sensor share 5 volt reference and ground terminals. Defective MAP sensor or harness can set "G" sensor DTC. Check scan tool FAILURE RECORDS to determine mileage since last DTC was set.

1. Perform On-Board Diagnostic (OBD) System Check. Read and record FREEZE FRAME and/or FAIL RECORDS data for each DTC set. Go to next step.
2. If DTC P1392 is set, diagnose it first before proceeding. If no other DTC is set, go to next step.
3. Check for a poor connection at "G" sensor harness connector. If a problem is found, go to step 8). If no problem is found, go to next step.
4. Ensure ignition is off. Disconnect harness connectors from PCM and "G" sensor. Using DVOM, check "G" sensor signal circuit for an intermittent open or short to ground. If a problem was found, go to step 9). If no problem is found, go to next step.
5. Check reference circuit between PCM, MAP or "G" sensor for an intermittent short to ground. If a problem is found, go to step 9). If no problem is found, go to next step.
6. Check for poor 5-volt reference circuit terminal connection at PCM. If a problem is found, go to step 8). If no problem is found, go to next step.
7. Check for an intermittent open or a faulty splice in 5-volt reference circuit. If a problem is found, go to step 9). If no problem is found, check for an intermittent problem, see DIAGNOSTIC AIDS .
8. Repair 5-volt reference circuit and "G" sensor signal circuit harness connector terminals as necessary. Retest system.
9. Repair intermittent open or short circuit in wiring harness as necessary. Retest system.

Isuzu Trooper Limited 1997 - DTC P1391 - "G" SENSOR CIRCUIT PERFORMANCE Diagnostic Aids

An intermittent problem can be caused by misrouted harness, rubbed-through wire insulation or broken wire inside insulation. If connections and wiring appear okay, monitor scan tool "G" sensor display while moving sensor connections and related harnesses. Change in scan tool display will indicate area of fault. MAP and "G" sensor share 5 volt reference and ground terminals. Defective MAP sensor or harness can set "G" sensor DTC. Check scan tool FAILURE RECORDS to determine mileage since last DTC was set.

1. Perform On-Board Diagnostic (OBD) System Check. Read and record FREEZE FRAME and/or FAIL RECORDS data for each DTC set. Go to next step.
2. Turn ignition on. Using scan tool, read and record FAIL RECORDS data for DTC P1391. Operate vehicle within conditions noted in FAIL RECORDS data. Using scan tool, read SPECIFIC DTC. If scan tool displays DTC P1391 FAILED THIS IGN, go to step 4). If scan tool does not display DTC P1391 FAILED THIS IGN, go to next step.
3. Check for "G" sensor seal missing, damaged or mounting flanges cracked, missing or incorrectly installed. If problem is found, repair as necessary. Retest system. If no problem is found, check for an intermittent problem, see DIAGNOSTIC AIDS .
4. Disconnect "G" sensor electrical connector. Using scan tool, observe "G" sensor value. If value is about zero volts, go to next step. If value is not as specified, go to step 12).
5. Connect jumper wire between "G" sensor reference and signal circuit at harness connector. Using scan tool, read "G" sensor value. If "G" sensor value is about 4.95 volts, go to next step. If value is not as specified, go to step 7).
6. Turn ignition off. Disconnect PCM connector. Check sensor ground circuit for high resistance, poor connection at PCM or an open between PCM and "G" sensor. If no problem is found, go to step 10). If a problem is found, repair as necessary. Retest system.
7. Check 5-volt reference circuit for high resistance, open between PCM and "G" sensor or a poor connection at PCM. If a problem is found, repair as necessary. Retest system. If no problem is found, go to next step.
8. Check signal circuit for high resistance, open, short to ground or short to sensor ground. If a problem is found, repair as necessary. Retest system. If no problem is found, go to next step.
9. Check "G" sensor circuit for poor connection at PCM. If a problem is found, repair as necessary. Retest system. If no problem is found, go to step 13).
10. Check for poor connection at "G" sensor. If a problem is found, repair as necessary. Retest system. If no problem is found, go to next step.
11. Replace "G" sensor. Retest system.
12. With ignition off, disconnect PCM. Turn ignition on. Check "G" sensor signal circuit for a short to voltage or short to 5-volt reference circuit. If a problem is found, repair as necessary. Retest system. If no problem is found, go to next step.
13. Replace PCM. Retest system.

Isuzu Trooper Limited 1997 - DTC P1392 - "G" SENSOR CIRCUIT LOW VOLTAGE Diagnostic Aids

An intermittent problem can be caused by misrouted harness, rubbed-through wire insulation or broken wire inside insulation. If connections and wiring appear okay, monitor scan tool "G" sensor display while moving sensor connections and related harnesses. Change in scan tool display will indicate area of fault. MAP and "G" sensor share 5 volt reference and ground terminals. Defective MAP sensor or harness can set "G" sensor DTC. Check scan tool FAILURE RECORDS to determine mileage since last DTC was set.

1. Perform On-Board Diagnostic (OBD) System Check. Read and record FREEZE FRAME and/or FAIL RECORDS data for each DTC set. Go to next step.
2. Turn ignition on, engine off. Disconnect "G" sensor electrical connector. Using scan tool, observe "G" sensor value. If value is about zero volts, go to step 4). If value is not as specified, see ENGINE CRANKS BUT WILL NOT RUN in BASIC TESTING article.
3. Turn ignition on. Using scan tool, read and record FAIL RECORDS data for DTC P1392. Operate vehicle within conditions noted in FAIL RECORDS data. Using scan tool, read SPECIFIC DTC. If scan tool displays DTC P1392 FAILED THIS IGN, go to next step. If scan tool does not display DTC P1392 FAILED THIS IGN, check for an intermittent problem, see DIAGNOSTIC AIDS .
4. Disconnect "G" sensor electrical connector. Connect jumper wire between "G" sensor 5-volt reference and signal circuit at harness connector. Using scan tool, read "G" sensor value. If "G" sensor value is about 4.95 volts, go to step 9). If value is not as specified, go to next step.
5. Turn ignition off. Disconnect PCM and check 5-volt reference circuit for an open or short to ground. If a problem is found, repair as necessary. Retest system. If no problem is found, go to next step.
6. Check 5-volt reference circuit for a poor connection at PCM. If a problem is found, repair as necessary. Retest system. If no problem is found, go to next step.
7. With ignition off, disconnect PCM. Check "G" sensor signal circuit for open, short to ground or short to sensor ground. If a problem is found, repair as necessary. Retest system. If no problem is found, go to next step.
8. Check "G" sensor signal circuit for a poor connection at PCM. Repair as necessary. Retest system. If no problem is found, go to next step.
9. Replace PCM. Retest system.

Isuzu Trooper Limited 1997 - DTC P1393 - "G" SENSOR CIRCUIT HIGH VOLTAGE Diagnostic Aids

An intermittent problem can be caused by misrouted harness, rubbed-through wire insulation or broken wire inside insulation. If connections and wiring appear okay, monitor scan tool "G" sensor display while moving sensor connections and related harnesses. Change in scan tool display will indicate area of fault. MAP and "G" sensor share 5 volt reference and ground terminals. Defective MAP sensor or harness can set "G" sensor DTC. Check scan tool FAILURE RECORDS to determine mileage since last DTC was set.

1. Perform On-Board Diagnostic (OBD) System Check. Read and record FREEZE FRAME and/or FAIL RECORDS data for each DTC set. Go to next step.
2. Start engine and allow it to idle. Using scan tool read "G" sensor value. If value is greater than 4.5 volts (+3G), go to step 4). If value is 4.5 volts or less, go to next step.
3. Turn ignition on. Using scan tool, read and record FAIL RECORDS data for DTC P1393. Operate vehicle within conditions noted in FAIL RECORDS data. Using scan tool, read SPECIFIC DTC. If scan tool displays DTC P1393 FAILED THIS IGN, go to next step. If scan tool does not display DTC P1393 FAILED THIS IGN, check for an intermittent problem, see DIAGNOSTIC AIDS .
4. Turn ignition on, engine off. Disconnect "G" sensor electrical connector. Using scan tool, observe "G" sensor value. If value is not as specified, go to step 6). If value is about zero volts (-1G), go to next step.
5. Connect a test light to battery positive terminal and probe sensor ground. If test light illuminates, go to step 7). If test light does not illuminate, go to step 9).
6. With ignition off, disconnect PCM. Turn ignition on, engine off. Check "G" sensor signal circuit for a short to voltage or short to 5-volt reference circuit. If a problem is found, repair as necessary. Retest system. If no problem is found, go to step 11).
7. Check for poor sensor ground terminal connection at "G" sensor electrical connector. If a problem is found, replace faulty terminal. Retest system. If no problem is found, go to next step.
8. Check for a poor sensor ground terminal connection at PCM. If a problem is found, replace faulty terminal. Retest system. If problem is not found, go to next step.
9. Using DVOM, check continuity of "G" sensor ground circuit. If resistance is greater than 5 ohms, repair open or poor connection. Retest system. If no problem is found, go to next step.
10. Replace PCM. Retest system.
11. Replace "G" sensor. Retest system.

Isuzu Trooper Limited 1997 - DTC P1394 - "G" SENSOR CIRCUIT INTERMITTENT HIGH VOLTAGE Diagnostic Aids

An intermittent problem can be caused by misrouted harness, rubbed-through wire insulation or broken wire inside insulation. If connections and wiring appear okay, monitor scan tool "G" sensor display while moving sensor connections and related harnesses. Change in scan tool display will indicate area of fault. MAP and "G" sensor share 5 volt reference and ground terminals. Defective MAP sensor or harness can set "G" sensor DTC. Check scan tool FAILURE RECORDS to determine mileage since last DTC was set.

1. Perform On-Board Diagnostic (OBD) System Check. Read and record FREEZE FRAME and/or FAIL RECORDS data for each DTC set. Go to next step.
2. If DTC P1393 is also set, repair P1393 first. If DTC P1393 is not set, go to next step.
3. If DTC P1106 and/or P1121 are also set, go to step 6). If DTC P1106 and/or P1121 are not set, go to next step.
4. Check for poor sensor ground terminal connection at "G" sensor electrical connector. If a problem is found, replace faulty terminal and go to step 9). If no problem is found, go to next step.
5. Check for an intermittent short to voltage in "G" sensor signal circuit between "G" sensor connector and PCM connector. If a problem is found, go to step 10). If no problem is found, go to step 8).
6. Check for an intermittent short to voltage in reference circuit between PCM and MAP sensor or "G" sensor. If a problem is found, go to step 10). If no problem is found, go to next step.
7. Check for a poor sensor ground circuit terminal connection at PCM. If a problem is found, go to step 9). If no problem is found, go to next step.
8. Check for an intermittent open or a faulty splice in sensor ground circuit. If a problem is found, go to step 10). If no problem is found, check for an intermittent problem, see DIAGNOSTIC AIDS .
9. Replace faulty harness connector terminal for sensor ground circuit. Retest system.
10. Locate and repair intermittent open or short circuit in wiring harness. Repair as necessary. Retest system.

Isuzu Trooper Limited 1997 - DTC P1406 - EGR VALVE PINTLE POSITION CIRCUIT Diagnostic Aids

An intermittent problem can be caused by misrouted harness, rubbed-through wire insulation or broken wire inside insulation. Monitor EGR actual position display while moving EGR connections and related harnesses. Change in scan tool display will indicate area of fault. Check scan tool FAILURE RECORDS to determine mileage since last DTC was set.

1. Perform On-Board Diagnostic (OBD) System Check. Read and record FREEZE FRAME and/or FAIL RECORDS data for each DTC set. Go to next step.
2. Turn ignition on, engine off. Using scan tool, read and record FAILS RECORD DATA. Operate vehicle within conditions noted in FAILED RECORDS DATA. Read SPECIFIC DTC. If scan tool displays DTC P1406 FAILED THIS IGN, go to next step. If scan tool does not display DTC P1406 FAILED THIS IGN, check for an intermittent problem, see DIAGNOSTIC AIDS .
3. Turn ignition off. Disconnect EGR valve harness connector. Inspect EGR valve and connector for damaged pins or terminals. Repair as necessary. If EGR valve and connector pins or terminals are okay, go to next step.
4. Reconnect EGR valve. Using scan tool, select MISC. TESTS, ENGINE OUTPUTS and EGR. Use up arrow to increase EGR position to 40 percent. If engine misses or stalls, go to step 14). If engine does not miss or stall, go to next step.
5. Disconnect EGR valve harness connector. Turn ignition on. Connect a test light between engine ground and EGR valve harness connector ignition feed circuit (Black/Yellow wire). If test light illuminates, go to step 7). If test light does not illuminate, go to next step.
6. Repair EGR valve ignition feed circuit open. Retest system.
7. Turn ignition off. Connect a DVOM between EGR harness connector control and ignition feed circuits. If resistance is not about 8.5 ohms, go to step 13). If resistance is about 8.5 ohms, go to next step.
8. Turn ignition on. Connect a test light between battery voltage and EGR valve harness connector control circuit (Yellow wire). If test light does not illuminate, go to step 11). If test light illuminates, go to next step.
9. Turn ignition off. Disconnect PCM connectors. Turn ignition on. Connect a test light between battery voltage and EGR valve harness connector control circuit (Yellow wire). If test light does not illuminate, go to step 12). If test light illuminates, go to next step.
10. Locate and repair short to ground in EGR control circuit. Retest system.
11. Check EGR control circuit for an open. If no open is found, go to step 13). If an open is found, repair as necessary. Retest system.
12. Replace PCM. Retest system.
13. Replace EGR valve. If DTC P1406 still fails scan tool SPECIFIC DTC test, replace PCM. If DTC P1406 passes scan tool SPECIFIC DTC test, retest system.
14. Start engine and allow to idle. Using scan tool, select MISC. TESTS, ENGINE OUTPUTS and EGR. If pintle position voltage is .50-.75 volts, go to step 13). If pintle position voltage is .50-.75 volts, go to next step.
15. Turn ignition off. Disconnect EGR valve harness connector. Using DVOM, measure resistance between sensor ground and 5 volt reference of EGR valve. If resistance is 5000-5500 ohms, go to next step. If resistance is not 5000-5500 ohms, go to step 13).
16. Turn ignition on. Using DVOM, measure voltage between ground and 5 volt reference wire of EGR harness connector. If voltage is 4-6 volts, go to step 20). If voltage is not 4-6 volts, go to next step.
17. Backprobe for voltage between ground and PCM harness connector terminal which supplies 5 volts for EGR valve. If voltage is 4-6 volts, repair open 5 volt reference circuit. If voltage is not 4-6 volts, go to next step.
18. Check for short in EGR 5-volt reference circuit between PCM and EGR. If a problem is found, repair as necessary. Retest system. If no problem is found, go to next step.
19. Turn ignition off. Disconnect PCM connectors. Inspect PCM and connector for damaged pins or terminals. Repair as necessary. If PCM and connector pins and terminals are okay, replace PCM and retest system.
20. Measure voltage between EGR sensor ground and 5 volt reference wire of EGR harness connector. If voltage is 4-6 volts, go to step 23). If voltage is not 4-6 volts, go to next step.
21. Turn ignition off. Disconnect PCM connectors. Using DVOM, check for open or shorted EGR sensor ground wire between EGR and PCM. Repair as necessary. Retest system. If EGR sensor ground wire is okay, go to next step.
22. Inspect PCM and connector for damaged pins or terminals. Repair as necessary. If PCM and connector pins and terminals are okay, replace PCM and retest system.
23. Using DVOM, measure resistance between sensor ground and pintle position pin of EGR valve. If resistance is not 1000-1250 ohms, go to step 13). If resistance is 1000-1250 ohms, go to next step.
24. Turn ignition on. Connect a test light between battery voltage and EGR valve harness connector pintle position circuit (Yellow/Red wire). If test light does not illuminate, go to step 26). If test light illuminates, go to next step.
25. Turn ignition off. Disconnect PCM connectors. Leave test light connected between battery voltage and EGR valve harness connector pintle position circuit. If test light illuminates, repair short to ground in pintle position circuit (Yellow/Red wire). If test light does not illuminate, go to next step.
26. Ensure ignition is off. Disconnect PCM connectors. Turn ignition on. Using DVOM, measure voltage between ground and pintle position circuit. If voltage is zero volts, go to step 13). If voltage is not zero volts, go to next step.
27. Check for short to voltage in pintle position circuit. If short to voltage was not found, go to step 13). If short to voltage was found, repair as necessary and retest system.

Isuzu Trooper Limited 1997 - DTC P1441 - EVAP SYSTEM FLOW DURING NON-PURGE Diagnostic Aids

An intermittent may be caused by a cracked or punctured EVAP canister, damaged or disconnected vacuum, vent or purge line. Check for poor connection, rubbed through wire insulation or a broken wire inside insulation. Inspect harness connectors for backed out terminals, improper mating, broken locks, improperly formed or damaged terminals, poor terminal-to-wire connection, and damaged harness. Monitor FUEL TANK VACUUM display while moving EVAP connections and related harnesses. Change in scan tool display will indicate area of fault. If DTC cannot be duplicated, check scan tool FAILURE RECORDS to determine mileage since last DTC was set.

1. Perform On-Board Diagnostic (OBD) System Check. See ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK. After performing OBD system check, go to next step.
2. Remove fuel cap. Using scan tool, observe FUEL TANK VACUUM. If pressure is zero in. H2O, go to next step. If pressure is more than zero in. H2O, see FUEL TANK PRESSURE SENSOR in SYSTEM/COMPONENT TESTS article.
3. Zero pressure and vacuum gauges on EVAP Pressure/Purge Cart (J41413). Reinstall fuel cap. Read and record FAIL RECORDS data for DTC P1441. Clear DTCs. Using scan tool, command EVAP vent solenoid ON (closed). Connect EVAP pressure/purge cart to EVAP service port. Using EVAP pressure/purge cart, attempt to pressurize EVAP system to 5 in. H2O. If specified pressure is not achieved, to step 5). If specified pressure is achieved, go to next step.
4. Maintain EVAP system pressure at 5 in. H2O. Using scan tool, read FUEL TANK VACUUM. If scan tool does not display -5 in. H2O, see FUEL TANK PRESSURE SENSOR in SYSTEM/COMPONENT TESTS article. If scan tool displays -5 in. H2O, go to next step.
5. Disconnect vacuum source line at engine for EVAP purge solenoid. Connect a vacuum pump to EVAP canister purge valve vacuum source fitting. Apply 15 in. Hg vacuum. If vacuum does not hold, go to step 7). If vacuum holds, go to next step.
6. Check EVAP canister purge valve vacuum hoses for correct routing. If vacuum hoses are routed incorrectly, repair as necessary and go to step 8). If vacuum hoses are routed correctly, check for an intermittent problem, see DIAGNOSTIC AIDS .
7. Replace EVAP canister purge valve. Retest system.
8. Start engine. Remove fuel cap. Using scan tool, command EVAP vent solenoid ON (closed) and EVAP purge solenoid OFF (0 percent). Reinstall fuel cap. Monitor scan tool FUEL TANK VACUUM display while holding engine speed at 2500 RPM. If pressure is zero in. H2O, repair is complete. If pressure is not zero in. H2O, return to last step completed and continue repair.

Isuzu Trooper Limited 1997 - DTC P1508 - IDLE AIR CONTROL (IAC) SYSTEM LOW RPM Diagnostic Aids

Check for poor connection, rubbed through wire insulation or a broken wire inside insulation at PCM and IAC motor. Inspect harness connectors for backed out terminals, improper mating, broken locks, improperly formed or damaged terminals, poor terminal-to-wire connection, and damaged harness. Ensure air intake system is not restricted. Check throttle body for blockage and carbon build up. Clean as necessary. Inspect for a large vacuum leak at brake booster or PCV. If DTC cannot be duplicated, check scan tool FAILURE RECORDS to determine mileage since last DTC was set.

1. Perform On-Board Diagnostic (OBD) System Check. See ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK. After performing OBD system check, go to next step.
2. Start and idle engine. Turn off all accessories. Using scan tool, select MISC TEST, then select IAC SYSTEM. Command engine speed up to 1500 RPM, down to 500 RPM, then back to 1500 RPM while monitoring ENGINE SPEED display. If ENGINE SPEED display remains within 50 RPM of desired value, for each RPM command, fault is not present, see DIAGNOSTIC AIDS . If engine speed is not within 50 RPM of desired value, go to next step.
3. Disconnect IAC valve. Install IAC Noid-Light (J 37027). Start engine. Command engine speed up to 1500 RPM, down to 500 RPM, then back to 1500 RPM while monitoring noid-light. If noid-light cycles Red and Green (never off), go to step 5). If noid-light does not cycle, go to next step.
4. Check all IAC circuits for open, short to ground or short to voltage. Repair as necessary. If circuits are okay, go to step 8).
5. Check throttle body for objects blocking IAC passage or throttle bore, excessive deposits in IAC passage, pintle, throttle bore or throttle plate. Check for restriction or vacuum leaks in air intake system. Check adjustment screw for tampering. Repair as necessary. If no problems are found, go to next step.
6. Check for poor terminal contact at IAC harness connector. Repair as necessary. If terminal contacts are okay, go to next step.
7. Replace IAC valve. Retest system.
8. Check IAC terminal contacts at PCM harness connector C1. Repair as necessary. If terminal contacts are okay, go to next step.
9. Replace PCM. Retest system.

Isuzu Trooper Limited 1997 - DTC P1509 - IDLE CONTROL SYSTEM HIGH RPM Diagnostic Aids

Check for poor connection, rubbed through wire insulation or a broken wire inside insulation at PCM and IAC motor. Inspect harness connectors for backed out terminals, improper mating, broken locks, improperly formed or damaged terminals, poor terminal-to-wire connection, and damaged harness. Ensure air intake system is not restricted. Check throttle body for blockage and carbon build up. Clean as necessary. Check for vacuum leak. If DTC cannot be duplicated, check scan tool FAILURE RECORDS to determine mileage since last DTC was set.

1. Perform On-Board Diagnostic (OBD) System Check. See ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK. After performing OBD system check, go to next step.
2. Start and idle engine. Turn off all accessories. Using scan tool, select MISC TEST, then select IAC SYSTEM. Command engine speed up to 1500 RPM, down to 500 RPM, then back to 1500 RPM while monitoring ENGINE SPEED display. If ENGINE SPEED display remains within 50 RPM of desired value, for each RPM command, fault is not present, see DIAGNOSTIC AIDS . If engine speed is not within 50 RPM of desired value, go to next step.
3. Disconnect IAC valve. Install IAC Noid-Light (J 37027). Start engine. Command engine speed up to 1500 RPM, down to 500 RPM, then back to 1500 RPM while monitoring noid-light. If noid-light cycles Red and Green (never off), go to step 5). If noid-light does not cycle, go to next step.
4. Check all IAC circuits for open, short to ground or short to voltage. Repair as necessary. If circuits are okay, go to step 8).
5. Check throttle body for objects blocking IAC passage or throttle bore, excessive deposits in IAC passage, pintle, throttle bore or throttle plate. Check for restriction or vacuum leaks in air intake system. Check adjustment screw for tampering. Repair as necessary. If no problems are found, go to next step.
6. Check for poor terminal contact at IAC harness connector. Repair as necessary. If terminal contacts are okay, go to next step.
7. Replace IAC valve. Retest system.
8. Replace PCM. Retest system.

Isuzu Trooper Limited 1997 - DTC P1618 - SERIAL PERIPHERAL INTERFACE (SPI) PCM INTERPROCESSOR COMMUNICATION ERROR

1. Perform On-Board Diagnostic (OBD) System Check. After performing OBD system check, go to next step.
2. If EEPROM calibration is latest version available, replace PCM. Retest system. If EEPROM calibration is not latest version, go to next step.
3. Reprogram PCM with latest available EEPROM calibration. Clear DTCs. If DTC P1618 resets, replace PCM. If DTC P1618 does not reset, repair is complete.

Isuzu Trooper Limited 1997 - DTC P1640 - OUTPUT DRIVER MODULE (ODM) "A" FAULT Diagnostic Aids

Check for poor connection, rubbed through wire insulation or a broken wire inside insulation each component. Inspect harness connectors for backed out terminals, improper mating, broken locks, improperly formed or damaged terminals, poor terminal-to-wire connection, and damaged harness. If DTC cannot be duplicated, check scan tool FAILURE RECORDS to determine mileage since last DTC was set.

1. Perform On-Board Diagnostic (OBD) System Check. After performing OBD system check, go to next step.
2. Turn ignition on, engine off. Using scan tool, select DATA LIST, SPECIFIC ENGINE and DRIVERS CURRENT. When DRIVER MODULE 1 STATUS is displayed select YES. Using YES button, cycle through all driver circuits. If a fault was indicated in any of drivers circuits, go to step 4). If a fault was not indicated in any of drivers circuits, go to next step.
3. Using scan tool, select DRIVERS HISTORY. Using YES button, cycle through all driver circuits. If a fault was not indicated in any of drivers circuits, replace PCM. Retest system. If a fault was indicated in any of drivers circuits, check for an intermittent problem, see DIAGNOSTIC AIDS .
4. Inspect fuse for faulty drivers circuit. If fuse is okay, go to step 6). If fuse was blown, go to next step.
5. Locate and repair short to ground between fuse and appropriate component. Replace fuse. Retest system.
6. Disconnect PCM connector of affected driver circuit. Inspect PCM and connector for damaged pins or terminals. Repair as necessary. If PCM and connector pins and terminals are okay, go to next step.
7. If none of drivers circuit faults were for CHECK ENGINE or CHECK TRANS, go to step 12). If any of drivers circuit faults were for CHECK ENGINE or CHECK TRANS, go to next step.
8. Turn ignition off. Disconnect PCM and turn ignition on. Using DVOM, measure voltage between affected light driver circuit at PCM harness connector and ground. If reading is about battery voltage, replace PCM. Retest system. If voltage is not as specified, go to next step.
9. Check for battery voltage to affected light driver circuit fuse. If voltage is as specified, go to next step. If voltage is not as specified, repair open circuit between ignition switch and fuse. Retest system.
10. Turn ignition off. Using DVOM, check for continuity between ground and affected driver terminal at PCM connector. If continuity exists, repair short to ground in affected driver circuit between affected component and PCM connector. Retest system. If continuity does not exist, go to next step.
11. Repair open in affected driver circuit between fuse and PCM connector. Retest system.
12. Reconnect PCM. Start engine and allow to idle. Using DVOM, backprobe affected terminal at PCM connector for battery voltage. If voltage is as specified, replace PCM. Retest system. If voltage is not as specified, go to next step.
13. Run engine at idle. Check for battery voltage to affected circuit fuse. If voltage is as specified, go to step 10). If voltage is not as specified, repair open circuit between ignition switch and fuse. Retest system.

Isuzu Trooper Limited 1997 - SUMMARY

If no hard fault codes are present, driveability symptoms exist or intermittent codes exist, proceed to TESTS W/O CODES article for diagnosis by symptom (i.e., ROUGH IDLE, NO START, etc.) or intermittent diagnostic procedures.