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Chevrolet Camaro Z28 1993 - G - TESTS W/CODES - 3.4L 1993 ENGINE PERFORMANCE General Motors Self-Diagnostics - 3.4L V6 ECM/PCM
Chevrolet Camaro Z28 1993 - INTRODUCTION
Most engine control problems are the result of mechanical breakdowns, poor electrical connections or damaged vacuum hoses. Before considering the computer system as a possible cause of problems, perform checks and inspections covered in BASIC TESTING article in this section. Failure to do so may result in lost diagnostic time.
If no faults were found while performing BASIC TESTING , proceed with DIAGNOSTIC PROCEDURE under SELF-DIAGNOSTIC SYSTEM. If no fault codes or only a non-running Code 12 is present and driveability problems exist, proceed to TESTS W/O CODES article in this section for diagnosis by symptom (i.e., ROUGH IDLE, NO START, etc.). If only intermittent codes are present, see INTERMITTENTS in TESTS W/O CODES article in this section.
Chevrolet Camaro Z28 1993 - SELF-DIAGNOSTIC SYSTEM
NOTE: Electronic Control Module (ECM) may also be referred to as Powertrain Control Module (PCM) in some diagnostic charts and figures. Terms are used interchangeably.
Control module is equipped with a self-diagnostic system, which detects system failures or abnormalities. When a malfunction occurs, control module will illuminate SERVICE ENGINE SOON light located on instrument panel. SERVICE ENGINE SOON light may also be referred to as the Malfunction Indicator Light (MIL). When malfunction is detected and light is turned on, a corresponding trouble code will be stored in control module memory. To retrieve stored codes, see RETRIEVING CODES (NON-SCAN) . Malfunctions are recorded as hard failures or as intermittent failures.
Chevrolet Camaro Z28 1993 - HARD FAILURES
Hard failures cause SERVICE ENGINE SOON light to glow and remain on until malfunction 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. If a sensor fails, control module will use a substitute value in its calculations to continue engine operation. In this condition, vehicle is functional, but it will most likely encounter degraded driveability.
Chevrolet Camaro Z28 1993 - INTERMITTENT FAILURES
Intermittent failures cause SERVICE ENGINE SOON light to flicker or glow and go out about 10 seconds after intermittent fault goes away. Corresponding trouble code, however, will be retained in control module memory. If related fault does not reoccur within 50 engine starts, related trouble code will be erased from control module memory. Intermittent failures may be caused by sensor, connector or wiring related problems. See INTERMITTENTS in TESTS W/O CODES article in this section.
Chevrolet Camaro Z28 1993 - DIAGNOSTIC PROCEDURE
Diagnosis of computerized engine control system should be performed in following order:
- Ensure all engine systems not related to computer system are operating properly. DO NOT proceed with testing unless all other problems have been repaired. DIAGNOSTIC CIRCUIT CHECK must be performed before using trouble code charts. See BASIC TESTING article in this section.
- If trouble codes were displayed (other than Code 12), determine whether codes are hard or intermittent trouble codes. Hard codes will cause SERVICE ENGINE SOON light to glow continuously while engine is running. See HARD OR INTERMITTENT TROUBLE CODE DETERMINATION . For diagnosing hard codes, proceed to appropriate trouble code chart. For diagnosing intermittent codes, proceed to INTERMITTENTS in BASIC TESTING article in this section. Exceptions are Code 13, 15, 24, 44 and 45 charts, which may be used to help diagnose intermittent codes.
- If no trouble codes were displayed and a driveability problem exists, refer to SYMPTOMS in TESTS W/O CODES article in this section. Doing so will identify proper system or component to check in I - SYS/COMP TESTS article in this section.
- After necessary repairs are made, clear trouble codes and perform FIELD SERVICE MODE CHECK in BASIC TESTING article in this section.
NOTE: For information on retrieving codes using a scan tester, refer to user and reference manuals supplied with tester. On Riviera, codes can also be retrieved through Electronic Climate Control Panel (ECCP). For additional information on Riviera ECCP function, see G - PCM/BCM TESTS W/ CODES article in this section.
Chevrolet Camaro Z28 1993 - RETRIEVING CODES (NON-SCAN)
NOTE: Inserting jumper wire into test and ground terminals of ALDL connector with engine running will cause fuel injected vehicles to enter field service mode. Flashes of SERVICE ENGINE SOON light will not indicate codes if this is done. See FIELD SERVICE MODE CHECK in BASIC TESTING article in this section.
- Turn ignition on. DO NOT start engine. SERVICE ENGINE SOON light should glow. Locate Assembly Line Data Link (ALDL) connector attached to control module wiring harness. Most ALDL connectors are located under dash on driver side of vehicle. For exact location of ALDL, see COMPONENT LOCATIONS in I - SYS/COMP TESTS article in this section. Insert jumper wire from terminal "B" (diagnostic test terminal) to terminal "A" (ground) of ALDL connector. See Fig. 1 .
- SERVICE ENGINE SOON light should begin to flash codes. Each code will be repeated 3 times. If codes are not flashed or SERVICE ENGINE SOON light does not glow, perform DIAGNOSTIC CIRCUIT CHECK in BASIC TESTING article in this section. To exit diagnostic mode, turn ignition off and remove jumper wire from ALDL connector.
Fig. 1: Chevrolet Camaro Z28 1993 - Component Locations - ALDL Connector Terminal ID
Chevrolet Camaro Z28 1993 - READING TROUBLE CODES
Control module stores component failure information under a related trouble code which can be recalled for diagnosis and repair. Trouble codes may be read by counting flashes of SERVICE ENGINE SOON light or by reading digital display on a scan tester. Scan tester is faster to use, more accurate and capable of reading information which otherwise would necessitate testing individual control module and sensor/solenoid connector terminals using a digital voltmeter. See SCAN TESTER USAGE and SCAN DATA .
NOTE: When using most scan testers, a time delay exists between serial data updates. For instantaneous response, a digital voltmeter must be used.
If scan tester is not available, reading flashes of SERVICE ENGINE SOON light is possible by grounding diagnostic test terminal "B" of ALDL with ignition on and engine off. See Fig. 1 . For example, "FLASH, FLASH, pause, FLASH, longer pause" identifies Code 21. First series of flashes is first digit of trouble code. Second series of flashes is second digit of trouble code. Trouble codes are displayed starting with lowest numbered code. Each code is displayed 3 times. Codes will continue to repeat as long as ALDL test terminal is grounded.
NOTE: Trouble codes will be recorded at various operating times. Some codes require operation of that sensor or switch for 5 seconds; others require operation for 5 minutes or longer at normal operating temperature, vehicle speed and load. Therefore, some codes may not set in a service bay operational mode and may require road testing vehicle in order to duplicate condition under which code will set.
Chevrolet Camaro Z28 1993 - TROUBLE CODE DEFINITION
Chevrolet Camaro Z28 1993 ECM/PCM TROUBLE CODE DEFINITION
Code No. Circuit Affected 12 (1) No RPM Reference Pulse 13 Oxygen Sensor Circuit Open Left Oxygen Sensor Circuit Open (Dual-Sensor Models) 14 Coolant Temperature Sensor Signal Voltage Low 15 Coolant Temperature Sensor Signal Voltage High 16 System Voltage Low 17 Camshaft Sensor 21 TPS Signal Voltage High 22 TPS Signal Voltage Low 23 MAT Sensor Signal Voltage High 24 Vehicle Speed Sensor 25 MAT Sensor Signal Voltage Low 32 EGR System Error 33 MAP Sensor Signal Voltage High 34 MAP Sensor Signal Voltage Low 35 IAC Idle Speed Error 36 24X Signal Error (3.4L "F" Body) 39 Clutch Switch Error (3.4L "F" Body & 3.4L "W" Body) 42 EST Circuit Open Or Grounded 43 ESC Error 44 Lean Exhaust Indication Left Lean Exhaust Indication (Dual-Sensor Models) 45 Rich Exhaust Indication Left Rich Exhaust Indication (Dual-Sensor Models) 46 Pass-Key Circuit ("F" Body) 51 Faulty PROM, MEM-CAL Or ECM/PCM 52 Faulty/Missing CAL-PAC Or MEM-CAL 53 System Overvoltage 54 Fuel Pump Voltage Low 55 ECM/PCM Error 61 Degraded O2 Sensor (3.4L Exc. "F" Body) A/C System Performance (3.4L "F" Body) 63 Right Oxygen Sensor Circuit Open (Dual-Sensor Models) 64 Right Oxygen Sensor Lean (Dual-Sensor Models) 65 Right Oxygen Sensor Rich (Dual-Sensor Models) 66 A/C Pressure Sensor ((2) 3.4L "W" Body) Low A/C Charge (3.4L "F" Body) 67 A/C Pressure Sensor (3.4L "F" Body) 69 A/C Compressor Relay (3.4L "F" Body) 70 High A/C Pressure (3.4L "F" Body) 71 Low A/C Temperature (3.4L "F" Body) 73 High A/C Temperature (3.4L "F" Body) 75, 76 Or 77 EGR Solenoid Error (3.4L "F" Body) 81 Brake Switch Error (3.4L "F" Body) 82 3X Signal Error (3.4L "F" Body) 85 PROM Error 86 Analog/Digital Error (3.4L "F" Body) 87 EEPROM Error
(1) Display of a Code 12 is normal when reference pulses are not being received by control module (engine not running).
(2) Except for California models.
NOTE: Use trouble code charts only if SERVICE ENGINE SOON light is illuminated (indicating a current problem exists). Exceptions are Code 13, 15, 24, 44 and 45 charts, which may be used to help diagnose intermittent codes. Anytime control module-related Codes 51, 52 or 55 are displayed with another code, start with 50-series code, and then proceed to lower numbered codes.
Chevrolet Camaro Z28 1993 - HARD OR INTERMITTENT TROUBLE CODE DETERMINATION
During any diagnostic procedure, determine if codes are hard failure codes or intermittent failure codes. Diagnostic charts will not usually help analyze intermittent codes. To determine hard codes and intermittent codes:
- Manually enter diagnostic mode. Read and record all stored trouble codes. Exit diagnostic mode, and clear trouble codes. See CLEARING TROUBLE CODES .
- Apply parking brake, and place transmission in Neutral or Park. Block drive wheels, and start engine. SERVICE ENGINE SOON light should go out. Run warm engine at specified curb idle for 2 minutes and note SERVICE ENGINE SOON light.
- If SERVICE ENGINE SOON light comes on, manually enter diagnostic mode. Read and record trouble codes. This will reveal hard failure codes. Codes 13, 15, 24, 44 and 45 may require a road test to reset hard failure after trouble codes were cleared.
- If SERVICE ENGINE SOON light does not come on, all stored trouble codes were intermittent failures, except as noted above.
Chevrolet Camaro Z28 1993 - CLEARING TROUBLE CODES
Turn ignition switch to ON position, and ground diagnostic test terminal "B" at ALDL connector. See Fig. 1 . Turn ignition switch to OFF position, and remove control module fuse from fuse block for 10 seconds. Replace fuse. Remove diagnostic terminal ground lead. If fuse cannot be located, pigtail at battery can be disconnected. When power to ECM is removed, degraded driveability may be exhibited until control module "relearns" optimum operational parameters.
Chevrolet Camaro Z28 1993 - ECM/PCM LOCATION
On most models, engine control module is located behind right or left side of dash or behind right or left kick panel. On Grand Prix and Lumina, control module is located on right side of engine compartment. See COMPONENT LOCATIONS in I - SYS/COMP TESTS article in this section.
Chevrolet Camaro Z28 1993 - DIAGNOSTIC MATERIALS Diagnostic Aids
Diagnostic aids (located in many trouble code charts) are additional tips used to help diagnose trouble codes when inspected circuit is okay. Diagnostic aids may help lead to a definitive solution to trouble code problem.
Chevrolet Camaro Z28 1993 - Field Service Mode Check
If ALDL test terminal "B" is grounded with engine running, SERVICE ENGINE SOON light will indicate operational mode of engine. This test confirms proper operation of fuel system and verifies "closed loop" operation. Clear codes and perform this test after any repair is completed. Field service mode check can be found by proceeding to FIELD SERVICE MODE CHECK in BASIC TESTING article in this section.
Chevrolet Camaro Z28 1993 - SPECIAL TOOLS (DIAGNOSTIC)
NOTE: A scan tester plugged into ALDL may be used to read trouble codes and check voltages in system on serial data line (terminal "E", or terminal "M" on P-4 systems). This can save a great deal of time. For additional information, see SCAN TESTER USAGE and SCAN DATA .
Computerized engine control system is most easily diagnosed using scan tester; however, other tools may aid in diagnosing problems if a scan tester is unavailable. These tools are a tachometer, test light, ohmmeter, digital voltmeter with 10-megohm input impedance (minimum), vacuum pump, vacuum gauge, fuel injector test lights and 6 jumper wires 6" long (one wire with female connectors at both ends, one wire with male connectors at both ends and 4 wires with male and female connectors at opposite ends). A test light, rather than a voltmeter, must be used when indicated by a diagnostic chart.
Chevrolet Camaro Z28 1993 - SCAN TESTER USAGE
NOTE: Before connecting scan tester to vehicle, diagnostic system should be checked to determine if system is operating properly and if information received will be accurate. This is done by performing DIAGNOSTIC CIRCUIT CHECK located in BASIC TESTING article in this section. If vehicle does not pass diagnostic circuit check, information received may be invalid.
Scan tester is a specialized tester which, when plugged into ALDL, can be used to diagnose on-board computer control systems by providing instant access to circuit voltage information without need to crawl under dash or hood to backprobe sensors and connectors.
Scan tester cuts down diagnostic time dramatically by furnishing input data (voltage signals) which can be compared to specification parameters. See SCAN DATA. They may also furnish information on output device (solenoids and motors) status. However, status parameters only indicate output signals have been sent to devices by control module; they do not indicate whether devices have responded properly to signal. Verify proper response at output device using a voltmeter or test light.
NOTE: Code 12 should always exist when ALDL is grounded with key on and engine not running, but it may not be indicated by all makes of scan testers.
A problem may exist even if trouble codes are not present. About 80 percent of driveability problems occur without trouble codes. Sensors that are out of specification will not set a trouble code but will cause driveability problems.
Using scan tester is easiest method of checking sensor specifications and other data parameters. Tester is also useful in finding intermittent wiring problems by wiggling wiring harnesses and connections (key on, engine off) while observing data parameters. See SCAN DATA.
NOTE: If erroneous voltage signals are suspected, verify tester information using a digital voltmeter and wiring schematic. If non-existent codes are displayed, turn ignition off, remove tester, turn ignition on and ground ALDL test terminal "B". Same codes flashed by SERVICE ENGINE SOON light should be indicated by scan tester.
Chevrolet Camaro Z28 1993 - SCAN DATA
NOTE: Information contained in following tables is typical of readings taken on vehicle with engine idling, upper radiator hose hot, closed throttle, transmission in Park or Neutral, "closed loop" status achieved and all accessories off (except as noted in tables). Data parameters are updated every 1 1/4 seconds. On systems using P-4 computers, parameter updates are more frequent. Not all devices and systems are used on all models; following lists only represent most commonly used parameters. For additional information, refer to owner manual furnished with tester.
Chevrolet Camaro Z28 1993 SCAN DATA - PORT FUEL INJECTION
Tester Position Units Measured Nominal Value A/C Clutch On/Off Off (On With A/C) A/C Request Yes/No No/Yes (With Request) AIR Divert Sol On/Off On (Air To Switching Sol.); Off (Air To Atmosphere) AIR Switching Sol. On/Off On (To Exhaust Manifold); Off (To Catalytic Converter) BARO Volts 3.0 - 4.5 Battery Voltage Volts 13.5 - 14.5 Block Learn Counts 118 - 138 (128 Normal) Canister Purge Sol On/Off On/Engine Cold (Idle Some) Clear Flood On/Off See Scan Tester Manual Coolant Fan On/Off Off Below 216?F (102?C) Coolant Temp. ?C 85 - 105? (Norm. Temperature) Crank RPM RPM 100 - 900 Cross Counts Counts 0 - 255 EGR Solenoid On/Off On When Energized EGR Duty Cycle 0 - 100% 0/Closed; 100/Fully Open Fan Relay On/Off On When Energized Fan Request On/Off On With Request Fuel Back-Up Yes/No Yes When Engaged IAC Counts 0 - 50 Ignition/Crank On/Off On With Ignition/Crank Injector Pulse Width Mil./Sec .8 - 3.0 INT (Integrator) Counts 110-145 (128 Normal) Knock Retard (ESC) Counts 0 - 255 Knock Signal Yes/No Yes When Knock Exists MAT ?C 10 - 90? MAP Volts 1.0 (Idle) to 4.5 (WOT) "Open/Closed Loop Status" Ol/Cl Closed/Open During Extended Idle O2 Sensor Millivolts 100 (Lean) To 999 (Rich) P/N Switch P/N/RDL Park/Neutral P/S Switch Norm/Hi Normal PROM I.D. PROM No. Original Factory Number RPM RPM Spec. +/-25 RPM Drive (A/T); Spec. +/-50 RPM Neut. (M/T) Spark Advance Degrees Varies TCC On/Off Off (On With Command) TPS Volts 1.25 (Idle) To 5.00 (WOT) Throttle Angle 0-100% 0 (Idle) To 110 (WOT) Trouble Codes Code No. No Codes Upshift Light (M/T) On/Off Off VSS Or MPH MPH 0 - Actual Water Injection On/Off On When Injecting 1st Gear Switch On/Off On/1st Gear Only 3rd Gear Switch On/Off On/3rd & 4th Gear 4th Gear Switch On/Off On/4th Gear
Chevrolet Camaro Z28 1993 - ECM/PCM CODE CHARTS
NOTE: In following diagnostic tests, schematics and illustrations are courtesy of General Motors Corp.
Chevrolet Camaro Z28 1993 - CODE 13 - OPEN OXYGEN SENSOR CIRCUIT
NOTE: The 3.4L (VIN S) engine is equipped with 2 oxygen sensors. On these models, Code 13 will set if the left sensor circuit is open. Code 63 will set if the right sensor circuit is open. Use this chart for Code 63 also and perform tests for applicable sensor.
NOTE: Test numbers refer to numbers on diagnostic chart.
- This tests if problem still exists. Vehicle cannot enter "closed loop" mode if oxygen sensor circuit is open. Code 13 indicates an open in O2 sensor circuit. Code will set if Engine is at normal operating temperature, neither Code 21 nor Code 22 is stored, oxygen sensor voltage is constant within a specified range (.34-.55 volt), throttle angle is greater than idle, a precalibrated amount of time has elapsed since start-up and all conditions have existed for a precalibrated amount of time.
- Determines if oxygen sensor, wiring or control module is at fault. If wiring is good, grounding oxygen sensor wire will cause .45 volt reference supplied by control module to pull low.
- This tests oxygen sensor circuit wiring. Use only a high impedance (10-megohm minimum) digital voltmeter.
Chevrolet Camaro Z28 1993 - Diagnostic Aids
Control module will not go into closed loop if Code 13 is set. Code 13 may set if vehicle runs out of fuel or stalls while vehicle is in motion. If oxygen sensor ground becomes loose, a false oxygen sensor reading will occur. This can result in a Code 13 being set. On models equipped with an oxygen sensor heating element, element resistance should be 3.5-14 ohms.
Chevrolet Camaro Z28 1993 CODE 13 ECM TERMINAL & CIRCUIT WIRING IDENTIFICATION
Application ECM Terminal Wire Color 3.4L (VIN S) "W " Body O2 Signal B21 Purple O2 Ground B20 Tan 3.4L (VIN S) "F" Body Left O2 Signal B21 Purple/White Left O2 Ground B20 Black/White Right O2 Signal B22 Purple Right O2 Ground B23 Black/White
Chevrolet Camaro Z28 1993 - CODE 14 - COOLANT TEMPERATURE SENSOR (SIGNAL VOLTAGE LOW)
NOTE: This chart assumes engine cooling system is functioning properly (not overheating). Test numbers refer to numbers on diagnostic chart.
- Code 14 indicates control module has seen low coolant sensor voltage signal (high temperature) at control module terminal for a precalibrated period of time. This checks if conditions for Code 14 still exist.
- This tests for grounded sensor signal line between control module and coolant sensor.
Chevrolet Camaro Z28 1993 - Diagnostic Aids
After engine is started, temperature should rise steadily to about 190?F (88?C) and then stabilize when thermostat opens. At normal operating temperature, signal voltage at control module terminal should be 1.5-2.0 volts. Check sensor for shifted calibration by using sensor TEMPERATURE-TO-RESISTANCE VALUES table. When Code 14 is set, control module will turn on electric cooling fan(s) if equipped.
Chevrolet Camaro Z28 1993 CODE 14 ECM TERMINAL & CIRCUIT WIRING IDENTIFICATION
Application ECM Terminal Wire Color 3.4L "W" Body CTS Signal C16 Yellow CTS Ground C10 Black 3.4L (VIN S) "F" Body CTS Signal A31 Yellow CTS Ground A17 Black
Chevrolet Camaro Z28 1993 TEMPERATURE-TO-RESISTANCE VALUES (1)
Temperature ?F (?C) Ohms 210 (100) 185 160 (70) 450 100 (38) 1800 70 (20) 3400 20 (-7) 13,500 0 (-18) 25,000 -40 (-40) 100,700
(1) Measure resistance across sensor terminals.
Chevrolet Camaro Z28 1993 - CODE 15 - COOLANT TEMPERATURE SENSOR (SIGNAL VOLTAGE HIGH)
NOTE: Test numbers refer to numbers on diagnostic chart.
- Code 15 indicates control module has seen high resistance in coolant sensor circuit. This could be due to high resistance (cold temperature) or high voltage at coolant sensor terminal at control module for a precalibrated period of time. This checks if conditions for Code 15 still exist.
- This test simulates a low voltage condition. If control module recognizes low voltage signal, scan tester will display greater than 130?C. This indicates control module and wiring are not at fault.
- This test determines if coolant sensor ground or signal circuit is open.
Chevrolet Camaro Z28 1993 - Diagnostic Aids
After engine is started, temperature should rise steadily to about 190?F (88?C) and then stabilize when thermostat opens. At normal operating temperature, voltage at control module sensor signal line should be 1.5-2.0 volts. Check sensor for shifted calibration by using sensor TEMPERATURE-TO-RESISTANCE VALUES table. When Code 14 is set, control module will turn on electric cooling fan(s) if equipped.
Chevrolet Camaro Z28 1993 CODE 15 ECM TERMINAL & CIRCUIT WIRING IDENTIFICATION
Application ECM Terminal Wire Color 3.4L "W" Body CTS Signal C16 Yellow CTS Ground C10 Black 3.4L (VIN S) "F" Body CTS Signal A31 Yellow CTS Ground A17 Black
Chevrolet Camaro Z28 1993 TEMPERATURE-TO-RESISTANCE VALUES (1)
Temperature ?F (?C) Ohms 210 (100) 185 160 (70) 450 100 (38) 1800 70 (20) 3400 20 (-7) 13,500 0 (-18) 25,000 -40 (-40) 100,700
(1) Measure resistance across sensor terminals.
Chevrolet Camaro Z28 1993 - CODE 16 - SYSTEM VOLTAGE LOW (3.4L "F" BODY)
Code 16 will set when ignition is on and engine speed is greater than 1000 RPM and the ECM is sensing ignition input voltage of less than 8 volts for more than 2 seconds.
NOTE: Test numbers refer to numbers on diagnostic chart.
- Test generator output to determine proper operation of voltage regulator. Run engine at greater than 1000 RPM and measure voltage across battery. If voltage reading is less than 8 volts, repair generator.
Chevrolet Camaro Z28 1993 - Diagnostic Aids
Check for intermittent by monitoring system voltage with a scan tester while wiggling related wiring. If an intermittent is induced, display will abruptly change. This may help to isolate location of problem.
Chevrolet Camaro Z28 1993 - CODE 17 - CAMSHAFT SENSOR ERROR (3.4L "F" BODY)
Camshaft sensor is a Hall Effect switch located on the front of the engine. Sensor sends signals to the ECM when cylinder No. 1 is on the intake stroke. Signal is used by ECM to synchronize sequential fuel injection. If cam signal is not received by ECM, ECM will pulse fuel injectors sequentially, but the fuel injectors may not be in sync with each intake valve opening. A loss of this signal, or any extra signals (false signals), at engine speeds greater than 500 RPM will cause ECM to set a Code 17.
NOTE: Test numbers refer to numbers on diagnostic chart.
- ECM performs a test for Code 17 when the engine is running or cranking. Code 17 will set when a cam pulse is missing on the first pass through the internal ECM self-test of the camshaft position sensor, or a cam pulse is missing for 3 seconds.
- By repeatedly tapping the starter, camshaft timing mark and camshaft position sensor will align with each other. At this point, voltage from sensor to ECM should drop to near zero volts temporarily. This indicates the camshaft sensor is capable of sending a signal to the ECM.
- Before replacing camshaft position sensor, inspect sensor for proper installation.
Chevrolet Camaro Z28 1993 - Diagnostic Aids
An intermittent cam reference signal can be caused by poor connection, cracked sensor or internal engine problems.
Chevrolet Camaro Z28 1993 - CODE 21 - THROTTLE POSITION SENSOR (SIGNAL VOLTAGE HIGH)
NOTE: Test numbers refer to numbers on diagnostic chart.
- This test checks if code is result of a hard failure or an intermittent condition.
- This test simulates a low-voltage condition. If control module recognizes change of state, control module and wiring are okay.
- This step isolates a faulty sensor, control module or open sensor ground circuit. If sensor ground is shared by another sensor, an accompanying code related to that sensor may exist.
Chevrolet Camaro Z28 1993 - Diagnostic Aids
A scan tester displays throttle position in volts. Closed throttle voltage should be low. Voltage should increase gradually to about 4.5 volts at a steady rate as throttle angle is increased. If code is intermittent, see INTERMITTENTS in TESTS W/O CODES article in this section.
Chevrolet Camaro Z28 1993 CODE 21 ECM TERMINAL & CIRCUIT WIRING IDENTIFICATION
Application ECM Terminal Wire Color 3.4L "W" Body TPS Signal C15 Dark Blue TPS Ground C10 Black TPS Reference C12 Gray 3.4L (VIN S) "F" Body TPS Signal A30 Dark Blue TPS Ground A17 Black TPS Reference B31 Gray
Chevrolet Camaro Z28 1993 - CODE 22 - THROTTLE POSITION SENSOR (SIGNAL VOLTAGE LOW)
NOTE: Test numbers refer to numbers on diagnostic chart.
- This test checks if code is result of a hard failure or an intermittent condition.
- This test simulates conditions for a Code 21. If control module recognizes change of state, control module and wiring are okay.
- This simulates a high signal voltage to check for an open in TPS signal line to control module. Scan tester should recognize this signal and display high TPS voltage.
Chevrolet Camaro Z28 1993 - Diagnostic Aids
A scan tester displays throttle position in volts. Closed throttle voltage should be low. Voltage should increase gradually to about 4.5 volts at a steady rate as throttle angle is increased. If code is intermittent, see INTERMITTENTS in TESTS W/O CODES article in this section.
Chevrolet Camaro Z28 1993 CODE 22 ECM TERMINAL & CIRCUIT WIRING IDENTIFICATION
Application ECM Terminal Wire Color 3.4L "W" Body TPS Signal C15 Dark Blue TPS Ground C10 Black TPS Reference C12 Gray 3.4L (VIN S) "F" Body TPS Signal A30 Dark Blue TPS Ground A17 Black TPS Reference B31 Gray
Chevrolet Camaro Z28 1993 - CODE 23 - MAT SENSOR (SIGNAL VOLTAGE HIGH)
NOTE: Test numbers refer to numbers on diagnostic chart.
- This checks if code is result of a hard failure or an intermittent condition. Code 23 will set if engine has been running for a precalibrated period of time, has reached operating temperature and signal voltage indicates a intake air temperature less than -22?F (-30?C).
- This simulates conditions for a Code 25. If scan tester displays a high temperature, control module and wiring are not at fault.
- This checks for continuity of sensor signal and ground circuits. If ground circuit is shared by other sensors and ground circuit is open, accompanying codes related to those sensors may be present.
Chevrolet Camaro Z28 1993 - Diagnostic Aids
If engine is allowed to cool overnight, coolant and MAT sensor values should be close to each other when measured by scan tester. Code 23 will result if signal and ground circuits become open. Check sensor for shifted calibration by using sensor TEMPERATURE-TO-RESISTANCE VALUES table.
Chevrolet Camaro Z28 1993 CODE 23 ECM TERMINAL & CIRCUIT WIRING IDENTIFICATION
Application ECM Terminal Wire Color 3.4L "W" Body MAT Signal C4 Tan MAT Ground C5 Black 3.4L (VIN S) "F" Body MAT Signal C29 Tan MAT Ground A1 Black
Chevrolet Camaro Z28 1993 TEMPERATURE-TO-RESISTANCE VALUES (1)
Temperature ?F (?C) Ohms 210 (100) 185 160 (70) 450 100 (38) 1800 70 (20) 3400 20 (-7) 13,500 0 (-18) 25,000 -40 (-40) 100,700
(1) Measure resistance across sensor terminals.
Chevrolet Camaro Z28 1993 - CODE 24 - VEHICLE SPEED SENSOR
Speed sensor, which is a Permanent Magnet (PM) generator, provides control module with vehicle speed information. PM generator, mounted in transmission, produces a pulsing AC voltage signal whenever vehicle speed is greater than 3 MPH. Voltage level and pulses increase with vehicle speed. Control module converts pulsing voltage to MPH, which is used by control module to calculate vehicle adjustments.
NOTE: Test numbers refer to numbers on diagnostic chart.
- Code 24 sets when MPH reads zero, transmission is not in Park or Neutral, engine speed indicates vehicle is in a cruise mode (1200-4400) RPM, TPS indicates closed throttle and MAP sensor senses high manifold vacuum. All of these conditions must be met for 2-5 seconds. PM generator only produces a voltage signal if drive wheels are turning greater than 3 MPH.
- Before replacing control module, PROM/MEM-CAL should be checked for correct application.
Chevrolet Camaro Z28 1993 - Diagnostic Aids
A faulty or misadjusted park/neutral switch may set a false Code 24. Use scan tester to check for proper signal in Drive while wiggling shifter. Code 24 may set if vehicle is power braked (brakes applied and throttle depressed) for more than 10 seconds.
Chevrolet Camaro Z28 1993 - CODE 25 - MAT SENSOR (SIGNAL VOLTAGE LOW)
NOTE: Test numbers refer to numbers on diagnostic chart.
- This checks if code is hard failure or intermittent condition. Code 25 will set if a MAT temperature greater than 266?F (130?C) is sensed for more than a precalibrated period.
- This simulates condition for Code 23. If control module recognizes open circuit and scan tester displays temperature of less than -30?C, control module and wiring are okay.
Chevrolet Camaro Z28 1993 - Diagnostic Aids
If engine is allowed to cool overnight, coolant temperature sensor and MAT sensor values should be close to each other when measured by a scan tester. A Code 25 will result if sensor signal circuit is shorted to ground. Check sensor for shifted calibration by using sensor TEMPERATURE-TO-RESISTANCE VALUES table.
Chevrolet Camaro Z28 1993 CODE 25 ECM TERMINAL & CIRCUIT WIRING IDENTIFICATION
Application ECM Terminal Wire Color 3.4L "W" Body MAT Signal C4 Tan MAT Ground C5 Black 3.4L (VIN S) "F" Body MAT Signal C29 Tan MAT Ground A1 Black
Chevrolet Camaro Z28 1993 TEMPERATURE-TO-RESISTANCE VALUES (1)
Temperature ?F (?C) Ohms 210 (100) 185 160 (70) 450 100 (38) 1800 70 (20) 3400 20 (-7) 13,500 0 (-18) 25,000 -40 (-40) 100,700
(1) Measure resistance across sensor terminals.
Chevrolet Camaro Z28 1993 - CODE 32 - EGR SYSTEM ERROR (3.4L "W" BODY)
Code 32 represents an EGR flow test error. During a closed throttle coast-down, ECM will cycle 3 internal EGR valve solenoids on and off individually while monitoring for changes in engine RPM and oxygen (O2) sensor activity.
NOTE: Test numbers refer to numbers on diagnostic chart.
- This test determine if power to EGR valve exists.
- This test will determine if an open circuit exists in EGR wiring or if EGR valve is at fault.
- This test will determine if a short to ground exists in any circuit going to EGR valve or if ECM is at fault.
Chevrolet Camaro Z28 1993 - CODE 33 - MAP SENSOR (SIGNAL VOLTAGE HIGH)
NOTE: Test numbers refer to numbers on diagnostic chart.
- This test confirms Code 33 and determines if it is result of a hard failure or an intermittent condition. Code 33 will set when voltage signal reading is too high for greater than a precalibrated period of time, TPS voltage indicates throttle is closed and neither Code 21 nor 22 is present.
- This step simulates conditions for a Code 34. If control module recognizes and sets Code 34, low MAP signal, control module and 5-volt reference and MAP signal circuits are not at fault. If ground circuit is shared with other sensors and ground circuit becomes open, additional codes related to these sensors may be set.
Chevrolet Camaro Z28 1993 - Diagnostic Aids
With ignition switch in ON position and engine stopped, manifold pressure is equal to atmospheric pressure and signal voltage will be high. Comparison of BARO readings from a known good vehicle using same sensor is a good way to check accuracy of suspect sensor. Readings should be same within .4 volt. Code 33 will result if ground circuit is open, MAP signal circuit is shorted to voltage or to 5-volt reference circuit.
Chevrolet Camaro Z28 1993 CODE 33 ECM TERMINAL & CIRCUIT WIRING IDENTIFICATION
Application ECM Terminal Wire Color 3.4L "W" Body MAP Signal C22 Light Green MAP Ground C5 Black MAP Reference C7 Gray 3.4L (VIN S) "F" Body MAP Signal A29 Light Green MAP Ground A1 Black MAP Reference B31 Gray
Chevrolet Camaro Z28 1993 - CODE 34 - MAP SENSOR (SIGNAL VOLTAGE LOW)
NOTE: Test numbers refer to numbers on diagnostic chart.
- This confirms Code 34 and determines if code was caused by a hard failure or an intermittent fault. Code 34 will set when ignition is on and MAP signal voltage is low. On some systems, engine must be running to set code.
- Jumpering MAP signal to 5-volt reference at MAP harness connector will determine if sensor is at fault or if a problem exists with control module or wiring.
- Scan tester may not display 12 volts. Control module recognizes voltage as greater than 4 volts (high MAP voltage signal), indicating control module and MAP signal circuit are not at fault.
Chevrolet Camaro Z28 1993 - Diagnostic Aids
With ignition switch in ON position and engine stopped, manifold pressure is equal to atmospheric pressure and signal voltage will be high. Comparing BARO readings with a known good vehicle using same sensor is a good way to check accuracy of suspect sensor. Readings should be same within .4 volt. A Code 34 will also result if 5-volt reference and MAP signal circuits are open or shorted to ground.
Chevrolet Camaro Z28 1993 CODE 34 ECM TERMINAL & CIRCUIT WIRING IDENTIFICATION
Application ECM Terminal Wire Color 3.4L "W" Body MAP Signal C22 Light Green MAP Ground C5 Black MAP Reference C7 Gray 3.4L (VIN S) "F" Body MAP Signal A29 Light Green MAP Ground A1 Black MAP Reference B31 Gray
Chevrolet Camaro Z28 1993 - CODE 35 - IAC IDLE SPEED ERROR WITHOUT TECH 1
Code 35 will set when closed throttle engine speed is 150 RPM greater or less than correct idle speed for 20 seconds.
NOTE: Test numbers refer to numbers on diagnostic chart.
- IAC driver is used to extend and retract IAC valve. Movement is verified by an engine speed change. If no change in speed occurs, valve can be retested when removed from throttle body.
- Checks IAC movement quality from step 1). Between 700-1500 RPM, engine speed should change smoothly with each flash of tester light in both extend and retract. If IAC valve is retracted beyond control range (about 1500 RPM), many flashes in extend position may occur before engine speed begins to drop. This is normal on certain engines. Fully extending IAC may cause engine to stall. This may be normal.
- Steps 1) and 2) verified proper IAC valve operation, while this step checks IAC circuits. Each light on node light should flash Red and Green while IAC valve is cycled. While sequence of color is not important, check circuits for faults beginning with poor terminal contacts if either light is off or does not flash Red and Green.
NOTE: For IAC reset procedure, see IDLE SPEED & MIXTURE in ADJUSTMENTS article in this section.
Chevrolet Camaro Z28 1993 - Diagnostic Aids
A slow, unstable idle may be caused by a system problem which cannot be overcome by IAC. Scan counts will be greater than 60 if idle is too low and zero counts if idle is too high. If idle is too high, stop engine. Fully extend IAC using driver. Start engine. If idle speed is greater than 800 RPM, look for possible vacuum leaks.
Chevrolet Camaro Z28 1993 - System Too Lean
If air/fuel ratio is too lean, idle speed may be either too high (check for vacuum leaks) or too low. Engine speed may vary up and down; disconnecting IAC may not help. Scan tester and/or digital voltmeter (10-megohm) will read an oxygen (O2) sensor output less than 300 mV (.3 volt). Check for low fuel pressure or water in fuel. A contaminated O2 sensor (caused by silicone) will produce lean air/fuel mixtures with an O2 sensor output fixed greater than 800 mV (.8 volt). This may also set Code 45.
Chevrolet Camaro Z28 1993 - System Too Rich
If air/fuel ratio is too rich, idle speed will be too low and scan tester counts will usually be greater than 80. System may be obviously rich, with Black smoke from exhaust pipe. Scan tester and/or voltmeter will read an O2 sensor voltage signal fixed greater than 800 mV (.8 volt). Look for high fuel pressure and injectors leaking or sticking. Remove IAC, and inspect bore for foreign material and evidence of IAC valve dragging bore.
Chevrolet Camaro Z28 1993 - Throttle Body
Remove IAC, and inspect bore for evidence of IAC valve dragging.
Chevrolet Camaro Z28 1993 - IAC Valve Connections
Inspect carefully for loose or corroded connections.
Chevrolet Camaro Z28 1993 - PCV Valve
An incorrect PCV valve may cause incorrect idle speed.
Chevrolet Camaro Z28 1993 - CODE 35 - IAC IDLE SPEED ERROR USING TECH I
Code 35 will set when closed throttle engine speed is 150 RPM greater or less than correct idle speed for 20 seconds.
NOTE: Test numbers refer to numbers on diagnostic chart.
- Tech 1 RPM control mode is used to extend and retract IAC valve. Movement is verified by an engine speed change. If no change in speed occurs, valve can be retested when removed from throttle body. If IAC valve is retracted beyond control range (about 1500 RPM), many flashes in extend position may occur before engine speed begins to drop. This is normal on certain engines. Fully extending IAC may cause engine to stall. This may be normal.
- This test uses Tech 1 to command IAC-controlled idle speed. Control module issues commands to obtain requested idle speed. Each light on node light should flash Red and Green while IAC valve is cycled. While sequence of color is not important, check circuits for faults beginning with poor terminal contacts if either light is off or does not flash Red and Green.
Chevrolet Camaro Z28 1993 - Diagnostic Aids
A slow, unstable idle may be caused by a system problem which cannot be overcome by IAC. Scan counts will be greater than 60 if idle is too low and zero counts if idle is too high. If idle is too high, stop engine. Fully extend IAC with driver. Start engine. If idle speed is greater than 800 RPM, look for possible vacuum leaks.
Chevrolet Camaro Z28 1993 - System Too Lean
If air/fuel ratio is too lean, idle speed may be either too high (check for vacuum leaks) or too low. Engine speed may vary up and down; disconnecting IAC may not help. Scan and/or digital voltmeter (10-megohm) will read an oxygen (O2) sensor output less than 300 mV (.3 volt). Check for low fuel pressure or water in fuel. A contaminated O2 sensor (caused by silicone) will produce lean air/fuel mixtures with an O2 sensor output fixed greater than 800 mV (.8 volt). This may also set Code 45.
Chevrolet Camaro Z28 1993 - System Too Rich
If air/fuel ratio is too rich, idle speed will be too low and scan tester counts will usually be greater than 80. System may be obviously rich, with Black smoke from exhaust pipe. Scan tester and/or voltmeter will read an O2 sensor voltage signal fixed greater than 800 mV (.8 volt). Look for high fuel pressure and injectors leaking or sticking. Remove IAC, and inspect bore for foreign material and evidence of IAC valve dragging bore.
Chevrolet Camaro Z28 1993 - Throttle Body
Remove IAC, and inspect bore for evidence of IAC valve dragging.
Chevrolet Camaro Z28 1993 - IAC Valve Connections
Inspect carefully for loose or corroded connections.
Chevrolet Camaro Z28 1993 - PCV Valve
An incorrect PCV valve may cause incorrect idle speed.
Chevrolet Camaro Z28 1993 - CODE 36 - 24X SIGNAL ERROR (3.4L "F" BODY)
The 24X crankshaft position sensor is used to improve spark during cranking and engine speeds up to 2000 RPM. Code 36 will set if the engine is running and the ECM detects 6 or more 24X crankshaft sensor reference pulses have not occurred. Code 36 diagnosis occurs once per ignition cycle.
NOTE: Test numbers refer to numbers on diagnostic chart.
- The 24X signal RPM should be the same as engine speed up to 2000 RPM, at which time it stops. This test determines if the ECM is putting out a 24X signal.
- If circuit No. 1800 is shorted to voltage, this could also lead to a faulty sensor.
- If circuit No. 632 is shorted to voltage, this will set both Code 17 and Code 36.
Chevrolet Camaro Z28 1993 - Diagnostic Aids
An intermittent 24X signal and Code 36 can be caused by poor connections. Visually and physically check connections.
Chevrolet Camaro Z28 1993 - CODE 39 - CLUTCH SWITCH ERROR
Clutch switch is normally closed when the clutch pedal is at rest. When clutch is depressed, switch will change from off status to on status. ECM runs a diagnostic test that looks for a change of state in the switch logic. If there is a failure in the clutch switch circuit, a Code 39 will set and the SERVICE ENGINE SOON light will illuminate. Code 39 will set when engine temperature is greater than 194?F (90?C), vehicle speed is greater than 40 MPH and clutch switch test fails 4 consecutive times in one ignition cycle.
NOTE: Test numbers refer to numbers on diagnostic chart.
- When clutch is depressed, switch should go from closed to open and status on a scan tester display should change from off to on.
- This test will check for a poor ground to clutch switch.
- This test will determine if clutch switch is being supplied with battery voltage or if circuit is shorted to ground.
Chevrolet Camaro Z28 1993 - Diagnostic Aids
If Code 39 is stored in memory and no problem is found, ensure clutch switch fastener is secure and is not sticking or binding. Clutch and cruise control share the same switch.
Chevrolet Camaro Z28 1993 - CODE 42, EST CIRCUIT OPEN OR GROUNDED
Code 42 indicates ECM has seen an open or short to ground in HEI EST or by-pass circuit.
NOTE: Test numbers refer to numbers on diagnostic chart.
- This test confirms Code 42 and determines if fault is a hard failure or intermittent condition.
- This test checks for a normal EST ground path through ignition module. If EST circuit is shorted to ground, reading will be less than 500 ohms.
- As test light voltage touches by-pass circuit, module should switch. This will cause ohmmeter to switch from hundreds of ohms to thousands of ohms. This test assures module "switched".
- If module did not switch, this tests for a short in EST circuit, an open in by-pass circuit and a faulty ignition module connection or module.
- This step confirms Code 42 is a faulty ECM and not an intermittent problem in EST or by-pass circuits.
Chevrolet Camaro Z28 1993 - Diagnostic Aids
Scan tester does not have ability to help diagnose a Code 42 problem. See INTERMITTENTS in TROUBLE SHOOTING - NO CODES article.
Chevrolet Camaro Z28 1993 - CODE 43 - ESC ERROR (WITHOUT ESC MODULE)
NOTE: Test numbers refer to numbers on diagnostic chart. If an audible knock is heard from engine at idle, repair internal engine problems before proceeding.
- If tapping on engine does not produce a knock signal on scan tester, try tapping engine closer to sensor before proceeding.
- ECM supplies a 5-volt reference signal on knock sensor line. With knock sensor connected, this signal is pulled low to about 2.5 volts. Knock signal, which is an AC signal, rides on this 2.5-volt DC signal.
- This test determines if knock sensor is faulty or if ESC portion of MEM-CAL is faulty.
Chevrolet Camaro Z28 1993 - Diagnostic Aids
Check knock sensor signal circuit for a potential open or short to ground. An open knock signal circuit would cause 5-volt reference to remain high at ECM knock signal terminal. A short to ground in knock signal circuit would cause 5-volt reference signal to pull low to near zero volts. Resistance to ground through knock sensor should be 3300-4500 ohms. Also check for proper installation of MEM-CAL.
Chevrolet Camaro Z28 1993 - CODE 44 - LEAN EXHAUST INDICATION
NOTE: The 3.4L (VIN S) engine is equipped with 2 oxygen sensors. On these models, Code 44 will set if the left sensor circuit is lean. Code 64 will set if the right sensor circuit is lean. Use this chart for Code 64 also and perform tests for applicable sensor.
O2 sensor acts like an open sensor circuit and produces no voltage when exhaust temperature is less than 600?F (316?C). An open sensor circuit or cold sensor causes "open loop" operation. Camaro and Firebird are equipped with 2 oxygen sensors. Code 44 will reflect a lean left O2 sensor; Code 64 will indicate a lean right O2 sensor. Perform test procedures for right or left sensor as necessary.
NOTE: Test number refers to number on diagnostic chart.
- Checks to see if O2 sensor is registering a lean condition. Code 44 is set when O2 sensor voltage signal at control module is low (less than .3 volt) for a precalibrated period and system is operating in "closed loop".
Chevrolet Camaro Z28 1993 - Diagnostic Aids
Using scan tester, observe Block Learn Memory (BLM) value at different RPMs. If conditions for a Code 44 exist, block learn value will be about 150.
Chevrolet Camaro Z28 1993 - O2 Sensor Wire
O2 sensor wire may be mispositioned and laying against exhaust manifold. Check for ground between sensor and wire connector.
Chevrolet Camaro Z28 1993 - Fuel Contamination
Water, even small amounts, near in-tank fuel pump inlet can be delivered to injector. Water may cause a lean exhaust and set Code 44.
Chevrolet Camaro Z28 1993 - Fuel Pressure
System will be lean if fuel pressure is low. If necessary, monitor fuel pressure while driving vehicle. For fuel pressure checking procedure, see BASIC TESTING article in this section.
Chevrolet Camaro Z28 1993 - Exhaust Leaks
If exhaust system has large leaks, exhaust system negative pressure pulses can cause outside air to be drawn into system and past O2 sensor. Vacuum or crankcase leaks can also cause a lean condition.
Chevrolet Camaro Z28 1993 - Misfire Or Stall
If engine misfires or stalls (including running out of fuel) while vehicle is moving, a Code 44 may set. If Code 44 is intermittent, see INTERMITTENTS in TESTS W/O CODES article in this section.
Chevrolet Camaro Z28 1993 CODE 44 ECM TERMINAL & CIRCUIT WIRING IDENTIFICATION
Application ECM Terminal Wire Color 3.4L "W" Body O2 Signal A16 Purple O2 Ground A22 Tan 3.4L (VIN S) "F" Body Left O2 Signal B21 Purple/White Left O2 Ground B20 Black/White Right O2 Signal B22 Purple Right O2 Ground B23 Black/White
Chevrolet Camaro Z28 1993 - CODE 45 - RICH EXHAUST INDICATION
NOTE: The 3.4L (VIN S) engine is equipped with 2 oxygen sensors. On these models, Code 45 will set if the left sensor circuit is rich. Code 65 will set if the right sensor circuit is lean. Use this chart for Code 65 also and perform tests for applicable sensor.
O2 sensor acts like an open sensor circuit and produces no voltage when exhaust temperature is less than 600?F (316?C). An open sensor circuit or cold sensor causes "open loop" operation.
Code 45 indicates a rich exhaust. Diagnosis should begin with fuel pressure, leaking injector, HEI shielding (ground), vapor canister fuel saturation, coolant sensor, MAP sensor, O2 sensor contamination and TPS intermittent output.
Camaro and Firebird are equipped with 2 oxygen sensors. Code 45 will reflect a rich left O2 sensor; Code 65 will indicate a rich right O2 sensor. Perform test procedures for right or left sensor as necessary.
NOTE: Test number refers to number on diagnostic chart.
- Test checks to see if O2 sensor is registering a rich condition. Code 45 is set when vehicle is at operating temperature (in "closed loop"), throttle angle is greater than idle, O2 sensor signal at control module is greater than .7 volt for a precalibrated period and time since engine start is one minute or more.
Chevrolet Camaro Z28 1993 - Diagnostic Aids
If other codes of lower number are set with Code 45, use those charts first. Malfunction in MAP or TPS sensor circuits can cause a Code 45 to set. If other codes are not set, Code 45, rich exhaust, is most likely caused by:
Chevrolet Camaro Z28 1993 - Fuel Pressure High
If fuel pressure is too high, air/fuel ratio will be rich. For fuel pressure checking procedure, see BASIC TESTING article in this section. Control module can compensate for slight increases, but a Code 45 will be set if air/fuel ratio becomes too rich.
Chevrolet Camaro Z28 1993 - Ignition Ground
If an open occurs on HEI ground circuit, HEI induced electrical "noise" may result, causing simulated reference pulses to be picked up by control module on reference line of EST harness. Additional pulses result in a higher than actual engine speed signal. Control module will increase injector pulse width ("on" time) to match increased RPM signal. Scan tester will show higher than actual RPM, which can help in diagnosing this problem.
Chevrolet Camaro Z28 1993 - Evaporative Fuel Canister
Fuel saturation of charcoal canister will cause a rich air/fuel ratio. If canister is full of fuel, check canister control valves and hoses.
Chevrolet Camaro Z28 1993 - MAP Sensor
An output causing control module to sense a higher than normal manifold pressure (low vacuum) can cause system to go rich. Disconnecting MAP sensor will allow control module to substitute a fixed value for MAP sensor. If condition disappears, substitute a different MAP sensor, and continue testing.
Chevrolet Camaro Z28 1993 - TPS
An intermittent TPS output will cause system to operate rich due to a false indication of engine acceleration.
Chevrolet Camaro Z28 1993 - O2 Sensor Contamination
O2 sensor contamination, caused by silicone in certain fuels or use of improper RTV sealant, may cause a White powdery coating to cover exterior of O2 sensor. False high signal voltage (low oxygen content sensed) produced is interpreted by control module as a rich mixture, causing control module to set Code 45.
Chevrolet Camaro Z28 1993 - EGR Problem
EGR valve sticking open at idle is usually accompanied by a rough idle and/or stalling.
Also check for shorted or leaking injector and fuel-contaminated oil. If Code 45 is intermittent, see INTERMITTENTS in TESTS W/O CODES article in this section.
Chevrolet Camaro Z28 1993 CODE 45 ECM TERMINAL & CIRCUIT WIRING IDENTIFICATION
Application ECM Terminal Wire Color 3.4L "W" Body O2 Signal A16 Purple O2 Ground A22 Tan 3.4L (VIN S) "F" Body Left O2 Signal B21 Purple/White Left O2 Ground B20 Black/White Right O2 Signal B22 Purple Right O2 Ground B23 Black/White
Chevrolet Camaro Z28 1993 - CODE 46 - PASS-KEY CIRCUIT (3.4L "F" BODY)
The PASS-Key system is designated to disable vehicle operation if the incorrect key or starting procedure is used. PASS-Key decoder module sends a signal to the ECM if the correct key is being used. If the proper signal does not reach the ECM, the ECM will not pulse the injectors, thus not allowing the vehicle to start. Code 46 will set if proper signal is not being received on fuel enable signal circuit to ECM when ignition is turned on.
NOTE: Test numbers refer to numbers on diagnostic chart.
- If engine cranks but does not start, it indicates the portion of the module which generates the signal to the ECM is not operating of fuel enable signal circuit is open or shorted to ground. If decoder module is found to be okay, ECM may be at faulty, but this not a likely condition.
- If Code 46 is stored and engine will not crank, it indicates that there is a Pass-Key problem or incorrect key or starting procedure is being used.
Chevrolet Camaro Z28 1993 - Pass-Key Diagnosis
NOTE: For complete system diagnosis, see appropriate ANTI-THEFT SYSTEM article in the ACCESSORIES/SAFETY EQUIPMENT Section.
PASS-Key is a sophisticated system that interfaces ECM and starter with a power source, decoder module, starter enable relay, ignition switch and instrument cluster. Check system for following common problems:
- Ensure ignition key resistor pellet is not cracked, dirty or coated. Ensure excess plastic does not exist around pellet contacts.
- Check ignition key pellet sensing contacts in ignition lock cylinder. Look into cylinder lock. If contacts are damaged or are not Silver in color, replace cylinder lock.
- Check related fuses.
- Check security indicator bulb in the instrument panel.
A defective resistor pellet within ignition key or incorrect resistance value of key (15 different assigned values) will prevent vehicle from starting. Key must be correct electrically and mechanically. If incorrect key is used to try to start vehicle, decoder will not allow vehicle to start for 2-4 minutes, even after correct key is inserted.
If starter enable relay must be replaced, check circuit to starter solenoid for possible short. A short may have caused relay to fail.
Chevrolet Camaro Z28 1993 - CODE 51 - FAULTY PROM/MEM-CAL
Ensure all pins are fully inserted in socket. If pins are okay, replace PROM/MEM-CAL, clear memory and recheck. If Code 51 reappears, replace control module.
Chevrolet Camaro Z28 1993 - CODE 52 - FAULTY CAL-PAK
Ensure all pins are fully inserted in socket. If pins are okay, replace CAL-PAK, clear memory and recheck. If Code 51 reappears, replace control module.
Chevrolet Camaro Z28 1993 - CODE 53 - SYSTEM OVERVOLTAGE
This code indicates a basic charging system problem. Code 53 will set when voltage at control module terminal is greater or less than specification for a precalibrated time. If voltage at ECM battery voltage terminal is not within specification, check and repair charging system.
Chevrolet Camaro Z28 1993 CHARGING SYSTEM SPECIFICATIONS
Engine Minimum Charge Maximum Charge 3.4L 10 16.5
Fig. 47: Chevrolet Camaro Z28 1993 - Component Locations - Code 53 Flow Chart - System Overvoltage
Chevrolet Camaro Z28 1993 - CODE 54 - FUEL PUMP VOLTAGE LOW (3.4L "F" BODY)
ECM monitors fuel pump pressure switch circuit voltage for fuel system adjustments. Signal is also used to store a trouble code if fuel pump relay is defective or fuel pump voltage is lost while engine is running. About 12 volts should exist on ECM fuel pump voltage monitor circuit for 2 seconds after ignition is turned on or any time reference pulses are being received by ECM.
Code 54 will set if voltage on voltage monitor circuit is low for 2-4 seconds since last reference pulse is cycled off. However, if voltage detected is low with engine running, light will only remain on while condition exists. If no fault is found, see INTERMITTENTS in TESTS W/O CODES article in this section.
Chevrolet Camaro Z28 1993 - CODE 54 - FUEL PUMP VOLTAGE LOW (3.4L "W" BODY)
Fuel pump circuit No. 120 is monitored and used by ECM for fuel system compensations based on system voltage. Signal is also used to store a trouble code if fuel pump relay is defective or fuel pump voltage is lost while engine is running. About 12 volts should exist on circuit No. 120 for 2 seconds after ignition is turned on or any time reference pulses are being received by ECM.
Code 54 will set if voltage on circuit No. 120 is less than 4 volts for .4 second since last reference pulse is cycled off; however, if voltage detected is less than 4 volts with engine running, light will only remain on while condition exists. If no fault is found, see INTERMITTENTS in TESTS W/O CODES article in this section.
Chevrolet Camaro Z28 1993 - CODE 55 - ECM ERROR
Ensure correct MEM-CAL or PROM is being used and that it is properly installed. If so, replace control module. Clear codes, confirm closed loop operation and check operation of SERVICE ENGINE SOON light.
Chevrolet Camaro Z28 1993 - CODE 61 - DEGRADED OXYGEN (O2) SENSOR (3.4L "W" BODY)
If a Code 61 is stored in memory, ECM has determined O2 sensor is contaminated or degraded because voltage change time (cross counts) is slow or sluggish.
ECM performs O2 sensor response time test when coolant temperature is more than 185?F (85?C), MAT temperature is greater than 50?F (10?C), system is in "closed-loop" or in a decel fuel cut-off mode. If Code 61 is stored, O2 sensor should be replaced.
Chevrolet Camaro Z28 1993 - CODE 61 - A/C SYSTEM PERFORMANCE (3.4L "F" BODY)
A/C refrigerant charge is calculated by inputs from the A/C refrigerant pressure and A/C evaporator temperature sensors. ECM will calculate system charge when the A/C is turned on. A/C evaporator temperature, A/C refrigerant temperature and vehicle speed are factored together to yield a minimum charge allowable for the A/C system to operate. If system charge falls below a given value for the temperature and vehicle speed variables, Code 61 will set. As ambient temperature falls, so does static (A/C off) refrigerant pressure. This produces a sliding scale which requires temperature, pressure and vehicle speed inputs to calculate a reliable system charge value that indicates when A/C refrigerant charge is too low to safely allow compressor to operate.
NOTE: Test numbers refer to numbers on diagnostic chart.
- This test determines if code is intermittent and will also check A/C system for other failures. Repair all other codes before proceeding. Use appropriate A/C service manual to verify proper gauge readings. Pressures vary with temperature and humidity.
- This test is to evaluate the A/C refrigerant pressure sensor for accuracy. A reliable gauge set should be used and no more than 20 psi difference in pressure between gauges and scan tester is allowable.
- System is operating though Code 61 is intermittent. Hardware failures should be investigated using appropriate A/C service section.
Chevrolet Camaro Z28 1993 - Diagnostic Aids
After a subsequent key cycle, the A/C will be enabled and Code 61 will be erased from current memory and stored as history. If input variables again indicate a low charge, the ECM will store a current Code 61 and disable the A/C clutch. Only after a relatively high number of failures occur will the A/C be disabled and become inoperative until the code is cleared, from both current and history code memory. The A/C status circuit allows the ECM to determine if the clutch is receiving a complete circuit via the A/C relay. If the status line is intermittently open or grounded, a Code 61 may set.
Chevrolet Camaro Z28 1993 - CODE 62 - GEAR SWITCH ERROR (3.4L "W" BODY)
2nd gear switch should be open in 2nd and 3rd gears. ECM uses this signal to disengage TCC when downshifting.
NOTE: Test numbers refer to numbers on diagnostic chart.
- Scan testers display switch status in different manners. - manufacturer operating manual to determine proper status display. Because both switches should be in same state during this test, tester should display same status for both 2nd and 3rd gear switches.
- Determines whether switch or signal circuit is open. Circuit can be checked for an open by measuring voltage at TCC connector. Reading should be about 12 volts.
- Because switches should be grounded in this step, disconnecting TCC connector should cause scan tester to change status.
- Switch status should change when vehicle shifts into 2nd gear.
Chevrolet Camaro Z28 1993 - Diagnostic Aids
If vehicle is road tested for a TCC-related problem, ensure switch status does not change in 3rd gear because TCC will disengage. If switches change status, carefully check wiring harness/routing and connectors.
Chevrolet Camaro Z28 1993 - CODE 63 - RIGHT OXYGEN SENSOR OPEN (3.4L "F" BODY)
See Code 13 chart and duplicate procedure for right O2 sensor as necessary.
Chevrolet Camaro Z28 1993 - CODE 64 - RIGHT OXYGEN (O2) SENSOR LEAN (3.4L "F" BODY)
See Code 44 chart and duplicate procedure for right O2 sensor as necessary.
Chevrolet Camaro Z28 1993 - CODE 65 - RIGHT OXYGEN (O2) SENSOR RICH (3.4L "F" BODY)
See Code 45 chart and duplicate procedure for right O2 sensor as necessary.
Chevrolet Camaro Z28 1993 - CODE 66 - A/C PRESSURE SENSOR (3.4L "W" BODY)
A/C pressure sensor responds to changes in A/C refrigerant system high side pressure. ECM uses A/C compressor load input to determine engine idle speed. Sensor uses a 5-volt reference signal from ECM and returns an input signal to ECM on a separate line. Low pressure (zero psi) will return a signal of about .1 volt. High pressure will return a signal of about 4.6 volts.
NOTE: Test numbers refer to numbers on diagnostic chart.
- Checks voltage signal from A/C pressure sensor to ECM.
- Checks to see if high signal is from a shorted sensor or a short to voltage in circuit. Normally, disconnecting sensor would make a normal circuit go to nearly zero volts.
- Checks to see if low voltage signal is from sensor or circuit. Jumpering sensor signal circuit to 5-volt reference checks circuit, connections and ECM.
- Checks to see if low voltage signal was due to an open in sensor circuit; previous step eliminated pressure sensor as a possible cause.
Chevrolet Camaro Z28 1993 - Diagnostic Aids
Code 66 sets when signal voltage falls outside normal sensor range and is not due to a A/C system problem. If problem is intermittent, check for opens or shorts in harness and poor connections. If wiring is okay, replace pressure sensor. If code resets, replace ECM.
Chevrolet Camaro Z28 1993 - CODE 66 - LOW A/C CHARGE (3.4L "F" BODY)
The A/C refrigerant pressure sensor responds to changes in A/C refrigerant system high side pressure. Input indicates how much load A/C compressor is putting on the engine and is one of the factors used by the ECM to determine IAC valve position for idle speed control, and engine cooling fan operation. The circuit consists of a 5-volt reference and a ground, both provided by the ECM, and a signal line to the ECM. The signal is a voltage which is proportional to the pressure. The sensor's range of operation is zero to 450 psi. At zero psi, the signal will be about .1 volt, varying up to about 4.9 volts at 450 psi or above. Code 66 sets if the voltage is less than one volt (approximately less than zero psi) for 5 seconds or more. The A/C compressor is disabled by the ECM if Code 66 is present or if pressure is greater than or less than calibrated values.
NOTE: Test numbers refer to numbers on diagnostic chart.
- This step checks the voltage signal being received by the ECM from the A/C refrigerant pressure sensor.
- Checks to see if low voltage signal is from the sensor or the circuit. Jumpering the sensor signal circuit to 5 volts checks the circuit, connections and ECM.
- This step checks to see if the low voltage signal was due to an open in the sensor signal circuit or the 5-volt reference circuit, since the proper step eliminated the pressure sensor.
Chevrolet Camaro Z28 1993 - Diagnostic Aids
Code 66 sets when signal voltage falls outside the normal possible range of the sensor and is not due to a refrigerant system problem. If problem is intermittent, check for opens or shorts in harness or poor connections.
Chevrolet Camaro Z28 1993 - CODE 67 - A/C PRESSURE SENSOR (3.4L "F" BODY)
ECM determines when A/C clutch is engaged by monitoring A/C status line. If A/C pressure does not increase by at least 9 psi when A/C clutch is turned on, Code 67 will set.
NOTE: Test numbers refer to numbers on diagnostic chart.
- Code 67 will set if ECM does not detect a A/C pressure increase of at least 9 psi when A/C clutch is engaged.
- If relay power feed is intermittent, A/C clutch status terminal may not detect voltage when A/C is commanded on.
- If A/C clutch status line becomes intermittently open or shorted while compressor is on, ECM will wrongly detect A/C clutch going on and off. When this occurs and clutch remains engaged, ECM will not detect pressure change and a Code 67 will be set.
- If A/C compressor clutch is disconnected or if A/C status circuit is open between splice and clutch, compressor clutch will not engage, but ECM will detect voltage on A/C status line, which will indicate clutch is on. If A/C switch is cycled on and off at this point, no pressure change will be detected and a Code 67 will set.
- The remaining tests check the A/C refrigerant pressure sensor circuit for proper operation.
Chevrolet Camaro Z28 1993 - Diagnostic Aids
A Code 67 will store in ECM memory but will not turn on the SERVICE ENGINE SOON light.
Chevrolet Camaro Z28 1993 - CODE 69 - A/C COMPRESSOR RELAY (3.4L "F" BODY)
When ECM detects A/C has been requested, ECM will activate the A/C clutch relay. When the relay has been activated, voltage should be present at both the A/C compressor clutch and the A/C clutch status line terminal of the ECM. If the ECM activates the A/C clutch relay but does not detect voltage present at the A/C status terminal for more than 10 seconds, Code 69 will set. An open or short to ground at any point in the A/C status circuit will cause Code 69 to set. A Code 69 fault will be stored in ECM memory but will not turn on the SERVICE ENGINE SOON light.
NOTE: Test numbers refer to numbers on diagnostic chart.
- Code 69 will set if the ECM has commanded the A/C on and no voltage is detected on the A/C status line after 20 seconds.
- If the A/C compressor clutch operates properly and scan tester indicates A/C status off, then an open exists between the ECM and the splice to the compressor.
Chevrolet Camaro Z28 1993 - CODE 70 - HIGH A/C PRESSURE (3.4L "F" BODY)
A/C pressure sensor responds to changes in A/C refrigerant system high side pressure. ECM uses A/C compressor load input to determine engine idle speed. Sensor uses a 5-volt reference signal from ECM and returns an input signal to ECM on a separate line. Low pressure (zero psi) will return a signal of about .1 volt. High pressure will return a signal of about 4.9 volts. ECM will disable A/C if Code 66 is present.
NOTE: Test numbers refer to numbers on diagnostic chart.
- This step checks the voltage signal being received by the ECM from the A/C refrigerant pressure sensor.
- Checks to see if the high voltage signal is from a shorted sensor or a short to voltage in the circuit. Normally, disconnecting the sensor would make a normal circuit go to near zero volts.
Chevrolet Camaro Z28 1993 - Diagnostic Aids
Code 70 sets when signal voltage falls outside of the normal possible range of the sensor and is not due to a refrigerant system problem. If problem is intermittent, check for opens or short in the harness or poor connections.
Chevrolet Camaro Z28 1993 - CODE 71 - LOW A/C TEMPERATURE (3.4L "F" BODY)
A/C temperature sensor is mounted to the evaporator, located within the instrument panel. The ECM receives a voltage signal inversely proportional to the temperature at the evaporator coils. As the evaporator temperature increases or decreases, the resistance of the sensor changes and varies the voltage signal to the ECM. This voltage is converted to a temperature value by the ECM and can then be displayed in degrees on a scan tester. A Code 71 fault will be stored in the ECM when evaporator temperature is less than -7?C but will not illuminate the SERVICE ENGINE SOON light.
NOTE: Test numbers refer to numbers on diagnostic chart.
- Code 71 will set if A/C evaporator temperature sensor indicates less than -7?C and time since start is 5 seconds or more.
Chevrolet Camaro Z28 1993 - Diagnostic Aids
Code 71 will set when signal voltage falls outside the normal range of the sensor and is not due to a refrigerant system problem. If problem is intermittent, check for opens or shorts in the harness or poor connections. A sensor which has backed out of the evaporator coil bracket will also set a false code.
Chevrolet Camaro Z28 1993 - CODE 73 - HIGH A/C TEMPERATURE (3.4L "F" BODY)
A/C temperature sensor is mounted to the evaporator which is located within the instrument panel. The ECM receives a voltage signal inversely proportional to the temperature at the evaporator coils. As the evaporator temperature increases or decreases, the resistance of the sensor changes and varies the voltage signal to the ECM. This voltage is converted to a temperature value by the ECM and can then be displayed in degrees on a scan tester. A Code 73 fault will be stored in the ECM when evaporator temperature is greater than 31?C but will not illuminate the SERVICE ENGINE SOON light.
NOTE: Test numbers refer to numbers on diagnostic chart.
- Code 73 will set if A/C evaporator temperature sensor indicates greater than 31?C and time since start is 5 seconds or more.
Chevrolet Camaro Z28 1993 - Diagnostic Aids
Code 73 will set when signal voltage falls outside the normal range of the sensor and is not due to a refrigerant system problem. If problem is intermittent, check for opens or shorts in the harness or poor connections.
Chevrolet Camaro Z28 1993 - CODE 75, 76 OR 77 - EGR SOLENOID ERROR (3.4L "F" BODY)
The ECM performs an EGR diagnostic check to monitor the flow of exhaust gases through the 3 EGR solenoids. When the vehicle is under deceleration, the EGR valves are normally closed. The ECM then opens each valve in succession (while keeping previous valves open) and manifold vacuum is monitored for a calculated MAP increase associated with each valve's application. Should the expected response of manifold vacuum not be seen by the ECM, a Code 75 (solenoid No.1), 76 (solenoid No. 2) or 77 (solenoid No. 3) will set.
NOTE: Test numbers refer to numbers on diagnostic chart.
- This test determines if there is power to the EGR valve.
- This test will determine if there is an open circuit in the EGR wiring or if the EGR valve is at fault.
- This test will determine if there is a short to ground in the solenoid drive circuits or if the ECM is at fault.
Chevrolet Camaro Z28 1993 - Diagnostic Aids
An intermittent may be caused by a poor connection, chafed wire insulation, or a wire broken inside insulation. Intake plenum should be checked for possible plugged passages.
Chevrolet Camaro Z28 1993 - CODE 81 - BRAKE SWITCH ERROR (3.4L "F" BODY)
ECM monitors the status of the brake switch circuit through the TCC/brake switch input. Code 81 will set if the vehicle speed has been greater than or equal to 35 MPH for 10 seconds and back to zero MPH for at least 4 occurrences and status of TCC/brake switch input has not changed from applied to release or released to applied as indicated on scan tester.
Chevrolet Camaro Z28 1993 - Diagnostic Aids
A Code 81 can be caused by a misadjusted brake switch or a poor connection. If the brake switch has failed in an open state, TCC will not engage.
Chevrolet Camaro Z28 1993 - CODE 82 - 3X SIGNAL ERROR (3.4L "F" BODY)
If scan tester did not indicate a cranking RPM, and there is no spark present at the plugs, the problem lies in the electronic ignition system or the power and ground supplies to the module. The magnetic crank sensor is used to determine engine crankshaft position much the same way as the pick-up coil did in the distributor type system. The sensor is mounted in the block near a 7-slot wheel on the crankshaft. The rotation of the wheel creates a magnetic field in the sensor which induces a voltage signal. The electronic ignition module then processes this signal and creates the reference pulses needed by the ECM and the signal triggers the correct coil at the correct time.
NOTE: Test numbers refer to numbers on diagnostic chart.
- This test will determine if the 12-volt supply and a good ground are available at the ignition module.
- Checks for resistance of the crank sensor and connections.
- Voltage will vary in this test depending on cranking speed of engine.
Chevrolet Camaro Z28 1993 - CODE 85 - PROM ERROR & CODE 87 - EEPROM ERROR
Ensure all ECM connectors are fully inserted in socket. If okay, have ECM reprogrammed using appropriate equipment. If equipment is not available, have ECM serviced through dealership.
Chevrolet Camaro Z28 1993 - CODE 86 - ANALOG/DIGITAL ERROR (3.4L "F" BODY)
If any other codes are present, use those charts first. The Analog/Digital (A/D) multiplexer chip is an internal part of the ECM. Some ECM sensor inputs lead to the A/D multiplexer. If any one of them shorts to battery voltage for more than 15 seconds, the A/D error diagnostic code will set, resulting in a Code 86.
Chevrolet Camaro Z28 1993 - Diagnostic Aids
If Code 86 is intermittent, all circuits leading to the ECM that are connected to the A/D multiplexer should be checked for an intermittent short to battery voltage. Monitor each input circuit on a scan tester and wiggle related circuits (wiring and connectors). Any circuit that intermittently shorts to battery voltage will show a change in data on the scan tester.
Chevrolet Camaro Z28 1993 - SUMMARY
If no hard fault codes are present, driveability symptoms exist or intermittent codes exist, proceed to TESTS W/O CODES article in this section for diagnosis by symptom (i.e., ROUGH IDLE, NO START, etc.) or intermittent diagnostic procedures.