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Chevrolet Corvette ZR-1 1994 - G - TESTS W/CODES 1994 ENGINE PERFORMANCE General Motors Corp. Self-Diagnostics
Chevrolet Corvette ZR-1 1994 - 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 Corvette ZR-1 1994 - SELF-DIAGNOSTIC SYSTEM
NOTE: Powertrain Control Module (PCM) is also be referred to as Electronic Control Module (ECM) 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 is 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 Corvette ZR-1 1994 - 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 Corvette ZR-1 1994 - 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 Corvette ZR-1 1994 - 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 TESTS W/O CODES article in this section.
- If no trouble codes are present and a driveability problem exists, refer to SYMPTOMS in TESTS W/O CODES article in this section. Doing so will help identify proper system or component to check in SYSTEM/COMPONENT 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.
Chevrolet Corvette ZR-1 1994 - RETRIEVING CODES (NON-SCAN)
Chevrolet Corvette ZR-1 1994 DATA LINK CONNECTOR (DLC) TEST TERMINALS
Application Ground/Test 16-Pin DLC (1)
(1) Tech 1 scan tester required to activate output/field service mode.
- Turn ignition on. DO NOT start engine. SERVICE ENGINE SOON light should glow. Locate DLC attached to control module wiring harness. Most DLC's are located under dash on driver side of vehicle. For exact location of DLC, see COMPONENT LOCATIONS in the SYSTEM/COMPONENT TESTS article in this section. Insert jumper wire from terminal "B" (diagnostic test terminal) to terminal "A" (ground) of DLC. 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 DLC connector.
Chevrolet Corvette ZR-1 1994 - 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" (if a wire is present) of DLC 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 DLC 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 Corvette ZR-1 1994 - TROUBLE CODE DEFINITION
Chevrolet Corvette ZR-1 1994 PCM TROUBLE CODE CONVERSION (1)
New No. Old No. Circuit P0101 34 MAF Sensor P0112 23 Air Temperature Sensor P0113 25 Air Temperature Sensor P0117 15 Coolant Temperature Sensor P0118 14 Coolant Temperature Sensor P0122 22 Throttle Position Sensor P0123 21 Throttle Position Sensor P0125 New Coolant Temperature Sensor P0131 44 Oxygen Sensor P0132 45 Oxygen Sensor P0134 13 Oxygen Sensor P0137 New (Catalyst) Oxygen Sensor P0138 New (Catalyst) Oxygen Sensor P0140 New (Catalyst) Oxygen Sensor P0171 New Fuel Lean P0172 New Fuel Rich P0300 New Misfire P0321 17 Spark Reference P0325 43 Knock Sensor P0341 18 Cam Signal P0342 41 Cam Signal P0401 53/54/55 EGR P0420 New Catalyst System P0501/0502 24 Vehicle Speed Sensor P0703 38 TCC Brake Switch P0705 31 Trans. Range Switch P0712 New Trans. Fluid Temp. Sensor P0713 New Trans. Fluid Temp. Sensor P0740 39 TCC P0755 36 Shift Solenoid "B" P1257 57 Supercharger Boost P1350/1361 42 Ignition P1403/1404/1405 75/76/77 EGR Solenoid(s) P1406 New EGR P1530 69 A/C Pressure Switch P1531 66 A/C Charge Low P1550 New Cruise P1558 63 Cruise P1561 61 Cruise P1562 62 Cruise P1565 65 Cruise P1567 67 Cruise P1568 68 Cruise P1571 New Traction Control P1573 New Traction Control P1599 99 Cruise P1619 New Oil Life Reset P1623 51 PROM Error P1626/1629 58 Pass-Key P1630 16 Voltage High/Low P1640 26/56 Quad-Driver P1650 26/56 Quad-Driver P1670 26/56 Quad-Driver code charts
(1) All P0 and P1 codes are located at the end of the pre-existing
NOTE: Use trouble code charts only if SERVICE ENGINE SOON light is illuminated (indicating a current problem exists).
Chevrolet Corvette ZR-1 1994 - 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:
- 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, enter diagnostic mode. Read and record trouble codes. This will reveal hard failure codes. Oxygen sensor related codes 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 Corvette ZR-1 1994 - CLEARING TROUBLE CODES
NOTE: On models not utilizing a 12-terminal DLC or if no wire is present in terminal "B", codes are cleared using a scan tester.
Turn ignition switch to ON position, and ground diagnostic test terminal "B" at DLC. 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 remove, degraded driveability may be exhibited until control module "relearns" optimum operational parameters.
Chevrolet Corvette ZR-1 1994 - ECM/PCM LOCATION
On Corvette, control module is located in left rear corner of engine compartment, next to battery. See COMPONENT LOCATIONS in SYSTEM/COMPONENT TESTS article in this section.
Chevrolet Corvette ZR-1 1994 - 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 Corvette ZR-1 1994 - Field Service Mode Check (If Available)
If DLC 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. Some models require the use of a scan tester to enter field service mode. Field service mode check can be found by proceeding to FIELD SERVICE MODE CHECK in BASIC TESTING article in this section.
Chevrolet Corvette ZR-1 1994 - SPECIAL TOOLS (DIAGNOSTIC)
NOTE: A scan tester plugged into DLC may be used to read trouble codes and check voltages in system on serial data line (terminal "E", or terminal "M"). 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 Corvette ZR-1 1994 - 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 DLC, 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.
Vehicles utilizing a 16-terminal DLC or 12-terminal DLC with terminal "B" not used, must use a scan tester for retrieving codes or enter Field Service Mode.
NOTE: Code 12 should always exist when DLC terminal "B" 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 calibration will not set a trouble code but will cause driveability problems.
Using a scan tester is the 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 DLC test terminal "B". Same codes flashed by SERVICE ENGINE SOON light should be indicated by scan tester.
Chevrolet Corvette ZR-1 1994 - 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 a minimum of 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 Corvette ZR-1 1994 MULTIPORT FUEL INJECTION (MFI)
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 (LT) Counts 118-138 (128 Normal) Canister Purge Sol. On/Off On/Engine Cold (Idle Some) Clear Flood On/Off See Tester Manual Coolant Fan(s) On/Off Off Below 216?F (102?C) Coolant Temp. ?C 85-105? (Norm. Temp.) 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 Integrator (ST) Counts 110-145 (128 Normal) Knock Retard Counts 0-255 Knock Signal Yes/No Yes When Knock Exists MAT (IAT) ?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 # 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) TP Sensor Volts 1.25 (Idle) To 5.00 (WOT) Throttle Angle 0-100% 0 (Idle) To 100 (WOT) Trouble Codes Code No. No Codes Upshift Light (M/T) On/Off Off VSS Or MPH MPH 0-Actual 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 Corvette ZR-1 1994 - ECM/PCM CODE CHARTS
NOTE: In following diagnostic tests, schematics and illustrations are courtesy of General Motors Corp.
Chevrolet Corvette ZR-1 1994 - CODE 11, MALFUNCTION INDICATOR LIGHT
MIL should always be on steady with ignition on and engine stopped. Ignition voltage is supplied directly to bulb. PCM turns on light by providing a path to ground.
NOTE: Test numbers refer to numbers on diagnostic chart.
- If MIL driver circuit or ignition feed circuit to bulb is open, MIL will not illuminate.
- Jumper Harness (J 35616-A) should be used instead of directly probing harness. This will prevent damage to harness.
- MIL should go off after engine starts. If it does, problem is not present at this time. If light does not go off, drive circuit is shorted to ground or PCM is faulty.
- If other codes are also displayed, use other code charts first, then restart at beginning of this chart.
Chevrolet Corvette ZR-1 1994 - Diagnostic Aids
If ignition feed circuit is suspected of being open, check and see if other bulbs on that circuit illuminate. Code 11 will cause MIL to remain on, even if malfunction clears.
Chevrolet Corvette ZR-1 1994 - CODE 13, OPEN OXYGEN SENSOR CIRCUIT
NOTE: 5.7L (VIN P) engine is equipped with 2 oxygen sensors. On Corvette, code 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. On some models oxygen sensors use a heating element. Heating element is not controlled by PCM.
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 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 Corvette ZR-1 1994 - Diagnostic Aids
Control module will not go into closed loop if code is set. Code 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 Corvette ZR-1 1994 CODE 13 PCM TERMINAL & CIRCUIT WIRING IDENTIFICATION
Application PCM Terminal Wire Color Left O2 Signal C20 Purple/White Left O2 Ground C19 Tan/White Right O2 Signal C8 Purple Right O2 Ground C7 Tan
Chevrolet Corvette ZR-1 1994 - CODE 14, COOLANT TEMPERATURE SENSOR SIGNAL VOLTAGE LOW
- For shared sensor ground tie-offs, see appropriate diagram in WIRING DIAGRAMS section.
NOTE: This chart assumes engine cooling system is functioning properly (not overheating). Test numbers refer to numbers on diagnostic chart.
- Code 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 still exist.
- This tests for grounded sensor signal line between control module and coolant sensor.
Chevrolet Corvette ZR-1 1994 - 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 is set, control module will turn on electric cooling fan(s) if equipped.
Chevrolet Corvette ZR-1 1994 CODE 14 PCM TERMINAL & CIRCUIT WIRING IDENTIFICATION
Application PCM Terminal Wire Color CTS Signal C25 Yellow CTS Ground B6 Black
Chevrolet Corvette ZR-1 1994 TEMPERATURE-TO-RESISTANCE VALUES (1)
Temperature ?F (?C) Ohms 212 (100) 177 194 (90) 241 158 (70) 467 104 (40) 1459 68 (20) 3520 23 (-5) 12,300 14 (-10) 16,180 0 (-18) 25,000 -4 (-20) 28,680 -22 (-30) 52,700 -40 (-40) 100,700
(1) Measure resistance across sensor terminals.
Chevrolet Corvette ZR-1 1994 - CODE 15, COOLANT TEMPERATURE SENSOR SIGNAL VOLTAGE HIGH
- For shared sensor ground tie-offs, see appropriate diagram in WIRING DIAGRAMS section.
NOTE: Test numbers refer to numbers on diagnostic chart.
- Code 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 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 Corvette ZR-1 1994 - 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 is set, control module will turn on electric cooling fan(s) if equipped.
Chevrolet Corvette ZR-1 1994 CODE 15 PCM TERMINAL & CIRCUIT WIRING IDENTIFICATION
Application PCM Terminal Wire Color CTS Signal C25 Yellow CTS Ground B6 Black
Chevrolet Corvette ZR-1 1994 TEMPERATURE-TO-RESISTANCE VALUES (1)
Temperature ?F (?C) Ohms 212 (100) 177 194 (90) 241 158 (70) 467 104 (40) 1459 68 (20) 3520 23 (-5) 12,300 14 (-10) 16,180 0 (-18) 25,000 -4 (-20) 28,680 -22 (-30) 52,700 -40 (-40) 100,700
(1) Measure resistance across sensor terminals.
Chevrolet Corvette ZR-1 1994 - CODE 16, OPTI-SPARK IGNITION SYSTEM LOW RESOLUTION PULSE
Ignition system supplies 2 timing inputs to PCM, a high resolution signal (360 pulses per camshaft revolution) and a low resolution signal (4 pulses per camshaft revolution). PCM can determine if either timing input is not being received by comparing inputs. If PCM detects high resolution pulse without detecting low pulse, Code 16 will set. Reference signal on resolution line toggles between zero and 5 volts as camshaft turns.
NOTE: Test numbers refer to numbers on diagnostic chart.
- If engine starts at this time, code is intermittent.
- This step determines if PCM is sending out a signal to distributor for processing. If this signal is not available or is shorted to ground or voltage, distributor cannot ground it to produce reference pulses.
Chevrolet Corvette ZR-1 1994 - Diagnostic Aids
An open, a short to voltage, a short to ground or a defective sensor inside distributor can prevent reference voltage from pulsing at PCM resolution terminal. If Code 16 does not reset and vehicle still does not start, go to NO START - ENGINE CRANKS OKAY in the BASIC TESTING article in this section.
Chevrolet Corvette ZR-1 1994 - CODE 18, INJECTOR CIRCUIT
Injectors are provided voltage when ignition is on. PCM energizes injectors by providing an individual ground for each injector. Injectors are energized on the intake stroke of each cylinder. PCM continuously monitors voltage on each driver circuit. When PCM detects a voltage that is out of range, Code 18 will set.
NOTE: Test numbers refer to numbers on diagnostic chart.
- Injector fuses are located in the underhood electrical center.
- Performing an injector balance test will determine which injector circuit is faulty.
- See mini-schematic to determine which fuse powers injector banks.
- When checking injector resistance, injector should be cold.
Chevrolet Corvette ZR-1 1994 - Diagnostic Aids
If an injector is disconnected and then reconnected while engine is running, injector driver is disabled for a predetermined time and Code 18 will set. When driver is disabled, an engine misfire will be evident.
Chevrolet Corvette ZR-1 1994 - CODE 21, THROTTLE POSITION SENSOR SIGNAL VOLTAGE HIGH
- For shared sensor ground tie-offs, see appropriate diagram in the WIRING DIAGRAMS section.
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 Corvette ZR-1 1994 - 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 Corvette ZR-1 1994 CODE 21 PCM TERMINAL & CIRCUIT WIRING IDENTIFICATION
Application PCM Terminal Wire Color TPS Signal C22 Dark Blue TPS Ground B6 Black TPS Reference B28 Gray
Chevrolet Corvette ZR-1 1994 - CODE 22, THROTTLE POSITION SENSOR SIGNAL VOLTAGE LOW
- For shared sensor ground tie-offs, see appropriate diagram in WIRING DIAGRAMS section.
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 setting code. 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 Corvette ZR-1 1994 - 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 Corvette ZR-1 1994 CODE 22 PCM TERMINAL & CIRCUIT WIRING IDENTIFICATION
Application PCM Terminal Wire Color TPS Signal C22 Dark Blue TPS Ground B6 Black TPS Reference B28 Gray
Chevrolet Corvette ZR-1 1994 - CODE 23, MAT SENSOR SIGNAL VOLTAGE HIGH
- For shared sensor ground tie-offs, see appropriate diagram in WIRING DIAGRAMS section.
NOTE: Test numbers refer to numbers on diagnostic chart.
- This checks if code is result of a hard failure or an intermittent condition. Code 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 setting code. 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 Corvette ZR-1 1994 - 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 will result if signal and ground circuits become open. Check sensor for shifted calibration by using sensor TEMPERATURE-TO-RESISTANCE VALUES table.
Chevrolet Corvette ZR-1 1994 CODE 23 PCM TERMINAL & CIRCUIT WIRING IDENTIFICATION
Application PCM Terminal Wire Color MAT Signal C21 Tan MAT Ground B16 Black
Chevrolet Corvette ZR-1 1994 TEMPERATURE-TO-RESISTANCE VALUES (1)
Temperature ?F (?C) Ohms 212 (100) 177 194 (90) 241 158 (70) 467 104 (40) 1459 68 (20) 3520 23 (-5) 12,300 14 (-10) 16,180 0 (-18) 25,000 -4 (-20) 28,680 -22 (-30) 52,700 -40 (-40) 100,700
(1) Measure resistance across sensor terminals.
Chevrolet Corvette ZR-1 1994 - 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 2 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.
NOTE: Prior to testing Corvette for Code 24, disable ASR system.
- 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 2 MPH.
- Before replacing control module, PROM/MEM-CAL should be checked for correct application.
Chevrolet Corvette ZR-1 1994 - 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 Corvette ZR-1 1994 - CODE 25, MAT SENSOR SIGNAL VOLTAGE LOW
- For shared sensor ground tie-offs, see appropriate diagram in WIRING DIAGRAMS section.
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 Corvette ZR-1 1994 - 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 Corvette ZR-1 1994 CODE 25 PCM TERMINAL & CIRCUIT WIRING IDENTIFICATION
Application PCM Terminal Wire Color Corvette MAT Signal C21 Tan MAT Ground B16 Black
Chevrolet Corvette ZR-1 1994 TEMPERATURE-TO-RESISTANCE VALUES (1)
Temperature ?F (?C) Ohms 212 (100) 177 194 (90) 241 158 (70) 467 104 (40) 1459 68 (20) 3520 23 (-5) 12,300 14 (-10) 16,180 0 (-18) 25,000 -4 (-20) 28,680 -22 (-30) 52,700 -40 (-40) 100,700
(1) Measure resistance across sensor terminals.
Chevrolet Corvette ZR-1 1994 - CODE 26, CANISTER PURGE SOLENOID
Solenoid is supplied voltage when ignition is on. PCM controls solenoid valve by providing a ground through one of its Quad-Drivers Modules (QDM). When solenoid is actuated, terminal is grounded and its monitored voltage will be low. When an output is off, its terminal voltage will be high. Each QDM has a separate fault line to indicate presence of a current fault to control module central processor.
NOTE: Test numbers refer to numbers on diagnostic chart.
- Code 26 will set if the PCM detects the wrong voltage potential. Test will determine if solenoid can be controlled by PCM.
- This check can detect a partially shorted coil which would cause excessive current flow. Excessive current flow to a QDM will be detected as a fault and set a code.
- The remaining checks will identify a circuit problem that has caused an excessive current flow or inoperative solenoid.
Chevrolet Corvette ZR-1 1994 - Diagnostic Aids
Check related harness connectors, including PCM harness. Check for damaged or pushed out terminals.
Chevrolet Corvette ZR-1 1994 - CODE 27, EGR SOLENOID VALVE
Ignition voltage is supplied voltage when ignition is on. PCM controls solenoid valve by providing a ground through one of its Quad-Drivers Modules (QDM). When solenoid is actuated, terminal is grounded and its monitored voltage will be low. When an output is off, its terminal voltage will be high. Each QDM has a separate fault line to indicate presence of a current fault to control module central processor.
NOTE: Test numbers refer to numbers on diagnostic chart.
- Code 27 will set if the PCM detects the wrong voltage potential. Test will determine if solenoid can be controlled by PCM.
- This check can detect a partially shorted coil which would cause excessive current flow. Excessive current flow to a QDM will be detected as a fault and set a code.
- The remaining checks will identify a circuit problem that has caused an excessive current flow or inoperative solenoid.
Chevrolet Corvette ZR-1 1994 - Diagnostic Aids
Check related harness connectors, including PCM harness. Check for damaged or pushed out terminals.
Chevrolet Corvette ZR-1 1994 - CODE 28, TRANSMISSION RANGE PRESSURE SWITCH
Transmission range pressure switch assembly consists of 5 pressure switches (2 normally closed, 3 normally open), and a fluid temperature sensor combined into one unit and mounted on the valve body. PCM supplies voltage to each range signal. By grounding one or more of these circuits through various combinations of pressure switches, PCM detects which manual valve position has been selected. With ignition on and engine off, Park/Neutral will be indicated. Code 28 will set when range signals "A" and "C" are both zero volts (on) for 2 seconds.
NOTE: Test numbers refer to numbers on diagnostic chart.
- Checks indicated range signal to valve position signal actually selected.
- Checks for correct voltage from PCM to transmission external connector.
- Checks for short to ground in any one of the 3 valve position circuits.
Chevrolet Corvette ZR-1 1994 - Diagnostic Aids
Code will set if PCM detects one of 2 illegal combinations. Check all connections for good contact.
Chevrolet Corvette ZR-1 1994 - CODE 29, SECONDARY AIR INJECTION
Ignition voltage is supplied voltage when ignition is on. PCM controls air pump relay by providing a ground through one of its Quad-Drivers Modules (QDM). When relay is actuated, terminal is grounded and its monitored voltage will be low. When an output is off, its terminal voltage will be high. Each QDM has a separate fault line to indicate presence of a current fault to control module central processor.
NOTE: Test numbers refer to numbers on diagnostic chart.
- Code 29 will set if the PCM detects the wrong voltage potential. Test will determine if relay can be controlled by PCM.
- This check can detect a partially shorted coil which would cause excessive current flow. Excessive current flow to a QDM will be detected as a fault and set a code.
- The remaining checks will identify a circuit problem that has caused an excessive current flow or inoperative relay.
Chevrolet Corvette ZR-1 1994 - Diagnostic Aids
Check related harness connectors, including PCM harness. Check for damaged or pushed out terminals.
Chevrolet Corvette ZR-1 1994 - CODE 33,
- For shared sensor reference and shared sensor ground tie -offs, see appropriate diagram in WIRING DIAGRAMS section.
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 Corvette ZR-1 1994 - 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 Corvette ZR-1 1994 CODE 33 PCM TERMINAL & CIRCUIT WIRING IDENTIFICATION
Application PCM Terminal Wire Color MAP Signal C23 Light Green MAP Ground B16 Black MAP Reference B29 Gray
Chevrolet Corvette ZR-1 1994 - CODE 34, MAP SENSOR SIGNAL VOLTAGE LOW
- For shared sensor reference and shared sensor ground tie -offs, see appropriate diagram in WIRING DIAGRAMS section.
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 Corvette ZR-1 1994 - 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 Corvette ZR-1 1994 CODE 34 PCM TERMINAL & CIRCUIT WIRING IDENTIFICATION
Application PCM Terminal Wire Color MAP Signal C21 Light Green MAP Ground B3 Black MAP Reference C7 Gray
Chevrolet Corvette ZR-1 1994 - CODE 35, IAC IDLE SPEED ERROR
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 Corvette ZR-1 1994 - 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 Corvette ZR-1 1994 - 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 Corvette ZR-1 1994 - 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 Corvette ZR-1 1994 - Throttle Body
Remove IAC, and inspect bore for evidence of IAC valve dragging.
Chevrolet Corvette ZR-1 1994 - IAC Valve Connections
Inspect carefully for loose or corroded connections.
Chevrolet Corvette ZR-1 1994 - PCV Valve
An incorrect PCV valve may cause incorrect idle speed.
Chevrolet Corvette ZR-1 1994 - CODE 36, OPTI-SPARK HIGH RESOLUTION PULSE
Ignition system supplies 2 timing inputs to PCM, a high resolution signal (360 pulses per camshaft revolution) and a low resolution signal (8 pulses per camshaft revolution). PCM can determine if either timing input is not being received by comparing inputs. If PCM detects low resolution pulse without detecting high pulse, Code 36 will set. Reference signal on resolution line toggles between zero and 5 volts as camshaft turns.
NOTE: Test numbers refer to numbers on diagnostic chart.
- Code will set if less than 60 high resolution timing pulses occur between each low resolution pulse and failure occurs 5 consecutive times.
- This step determines if PCM is sending out a signal to distributor for processing. If this signal is not available or is shorted to ground or voltage, distributor cannot ground it to produce reference pulses.
Chevrolet Corvette ZR-1 1994 - Diagnostic Aids
An open, a short to voltage, a short to ground or a defective sensor inside distributor can prevent reference voltage from pulsing at PCM resolution terminal. If Code 36 is present and vehicle still does not start, check for Code 16 and use that chart first. If vehicle still will not start, go to NO START - ENGINE CRANKS OKAY in BASIC TESTING article in this section.
Chevrolet Corvette ZR-1 1994 - CODE 37, TCC BRAKE SWITCH ERROR
PCM monitors activity of the normally-closed brake switch. Switch opens when brake pedal is applied.
NOTE: Test numbers refer to numbers on diagnostic chart.
- Checks for voltage at brake switch.
- Simulates brake switch closed or brakes off.
- Checks TCC brake switch circuit between PCM and switch.
Chevrolet Corvette ZR-1 1994 - Diagnostic Aids
Code 37 can be caused by a misadjusted brake switch or a poor connection. Code may also be set by unusual driving habits i.e. stop-and-go expressway driving.
Chevrolet Corvette ZR-1 1994 - CODE 38, TCC BRAKE SWITCH ERROR
PCM monitors activity of the normally-closed brake switch. Switch opens when brake pedal is applied.
NOTE: Test numbers refer to numbers on diagnostic chart.
- Checks for voltage at brake switch.
- Simulates brake switch closed or brakes off. Checks TCC brake switch circuit between PCM and switch.
- Checks circuit between TCC brake switch and PCM. Test opens TCC brake switch, simulating brakes applied.
Chevrolet Corvette ZR-1 1994 - Diagnostic Aids
Code may also be set by unusual driving habits i.e. stop-and-go expressway driving.
Chevrolet Corvette ZR-1 1994 - CODE 41, OPTI-SPARK IGNITION SYSTEM OPEN OR SHORTED EST CKT
Ignition system provides 2 timing inputs to PCM, high resolution (360 pulses per camshaft revolution) and low resolution (4 pulses per crankshaft revolution). PCM uses these 2 inputs to determine individual spark timing for each cylinder. Once PCM calculates ignition timing, timing signal will be sent to ignition coil driver on EST circuit. Each timing pulse received by ignition coil driver will trigger coil driver to operate ignition coil. EST signal voltage ranges from about .5 volt to 4.5 volts. If a Code 41 is set, PCM will disable fuel injectors to prevent flooding of engine.
NOTE: Test numbers refer to numbers on diagnostic chart.
- Determines if code is intermittent.
- This step determines if EST signal from PCM is available at ignition coil driver. EST circuit voltage should be between about .5 volt and 4.5 volts.
- Remaining steps ensure coil driver circuitry is okay. If all wiring and connections are okay, check ignition coil and ignition coil voltage supply.
Chevrolet Corvette ZR-1 1994 - Diagnostic Aids
Because coil driver gets its power from coil, check ignition feed circuit to ignition coil for opens.
Chevrolet Corvette ZR-1 1994 - CODE 42, IC CIRCUIT GROUNDED
Ignition system provides 2 timing inputs to PCM, high resolution (360 pulses per camshaft revolution) and low resolution (4 pulses per crankshaft revolution). PCM uses these 2 inputs to determine individual spark timing for each cylinder. Once PCM calculates ignition timing, timing signal will be sent to ignition coil driver on EST circuit. Each timing pulse received by ignition coil driver will trigger coil driver to operate ignition coil. EST signal voltage ranges from about .5 volt to 4.5 volts.
NOTE: Test numbers refer to numbers on diagnostic chart.
- If engine starts, code is intermittent.
- This test checks for an EST signal from PCM to ignition coil driver.
- Remaining tests check driver circuitry. Because coil driver gets its power from coil, check ignition coil feed circuit to ignition coil for opens.
Chevrolet Corvette ZR-1 1994 - CODE 43, KNOCK SENSOR CIRCUIT
The knock sensor informs the PCM of engine detonation. The PCM will retard ignition timing based on signals from the knock sensors. Knock sensors produce an AC voltage signal which is proportional to the amount of engine detonation (knock). Internal sensor circuitry causes the 5-volt DC reference signal sent by the PCM to be pulled low to about 1.5 volts. Any AC voltage produced by the sensors will travel to the PCM on this same reference line. Code 43 will set if: one sensor circuit becomes open, resulting in a 2.2 to 4.1-volt reference being monitored by the PCM, both sensor circuits become open, resulting in a reference voltage greater than 4.1 volts being seen by the PCM, or one or both circuits become grounded, resulting in a low (less than .78 volt) reference voltage being seen by PCM.
If an audible knock is heard from the engine, repair the internal engine problem, as normally no knock should be detected at idle. The PCM supplies 5 volts on the knock sensor circuit which should be present at the knock sensor terminals when the sensors are disconnected.
If knock sensor circuit is shorted to voltage, Code 43 will set. With both sensors and PCM disconnected, no voltage should be present. An improperly installed sensor can prevent the knock sensor from grounding to the block.
Chevrolet Corvette ZR-1 1994 - Diagnostic Aids
The PCM has the ability to diagnose opens and shorts on the knock sensor circuit. The scan tester will display if one or both sensors are open, or if both are grounded. Also, ensure knock sensor module is properly installed.
Chevrolet Corvette ZR-1 1994 - CODE 44, LEAN EXHAUST INDICATION
NOTE: Some models engines are 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. On models 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 Corvette ZR-1 1994 - 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. O2 Sensor Wire
O2 sensor wire may be mispositioned and laying against exhaust manifold. Check for ground between sensor and wire connector. 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 Corvette ZR-1 1994 - 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 Corvette ZR-1 1994 - 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. 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 Corvette ZR-1 1994 CODE 44 PCM TERMINAL & CIRCUIT WIRING IDENTIFICATION
Application PCM Terminal Wire Color Left O2 Signal C20 Purple/White Left O2 Ground C19 Tan/White Right O2 Signal C8 Purple Right O2 Ground C7 Tan
Fig. 52: Chevrolet Corvette ZR-1 1994 - Component Locations - Code 44 Flow Chart
Chevrolet Corvette ZR-1 1994 - CODE 45, RICH EXHAUST INDICATION
NOTE: On some models engines are 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.
On models using 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 Corvette ZR-1 1994 - 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 Corvette ZR-1 1994 - 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 Corvette ZR-1 1994 - 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 Corvette ZR-1 1994 - 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 Corvette ZR-1 1994 - 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 Corvette ZR-1 1994 - TPS
An intermittent TPS output will cause system to operate rich due to a false indication of engine acceleration.
Chevrolet Corvette ZR-1 1994 - 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 Corvette ZR-1 1994 - 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 Corvette ZR-1 1994 CODE 45 PCM TERMINAL & CIRCUIT WIRING IDENTIFICATION
Application PCM Terminal Wire Color Left O2 Signal C20 Purple/White Left O2 Ground C19 Tan/White Right O2 Signal C8 Purple Right O2 Ground C7 Tan
Chevrolet Corvette ZR-1 1994 - CODE 47, KNOCK SENSOR MODULE
Knock sensor module is located inside PCM.
Chevrolet Corvette ZR-1 1994 - CODE 48, MASS AIRFLOW SENSOR
Mass airflow meter measures amount of induction airflow. This information is used by PCM to determine adjustments to air/fuel ratio. MAF sensor is a hot-wire type. Sensor maintains hot wire at a predetermined temperature. The greater the airflow across the hot wire, the more current is required to maintain hot wire temperature. Sensor changes the current requirements into a frequency signal which is read by the PCM. The PCM calculates airflow based upon this signal.
NOTE: Test numbers refer to numbers on diagnostic charts.
- Determines if fault is a hard failure or an intermittent condition.
- Checks for 5-volt reference from PCM.
- Verifies both ignition voltage and a good ground circuit are available.
Chevrolet Corvette ZR-1 1994 - Diagnostic Aids
An intermittent may be caused by a poor connection, mis-routed harness, rubbed through wire insulation or a broken wire inside insulation. Code 48 could be caused by a vacuum leak. Check short and long term fuel trim for being in optimum range (both banks).
Chevrolet Corvette ZR-1 1994 - CODE 50, SYSTEM VOLTAGE LOW
PCM monitors voltage on ignition feed circuit (Pink wire). Normal voltage is 9.6-16 volts. If voltage drops below 8 volts, Code 50 will set and Malfunction Indicator Light (MIL) will illuminate.
Chevrolet Corvette ZR-1 1994 - Diagnostic Aids
An open in ignition feed circuit (Pink wire) or extremely low voltage may cause loss of serial data, no start condition and malfunction of the MIL. Additional codes may be set.
Chevrolet Corvette ZR-1 1994 - 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 Corvette ZR-1 1994 - 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 Corvette ZR-1 1994 - CODE 52, LOW ENGINE OIL TEMPERATURE
Engine oil temperature sensor is a thermistor, similar to a coolant or air temperature sensor. When engine oil temperature is cold, sensor resistance is high and PCM will see a high monitored voltage signal on engine oil temperature sensor signal terminal. As temperature increases, resistance decreases and PCM sees a lower monitored voltage on circuit.
NOTE: Test numbers refer to numbers on diagnostic chart.
- Code 52 will set if engine oil temperature sensor indicates less than -31?F (-35?C) and engine has been running for more than 30 minutes.
- Code 52 will set when open occurs in sensor, wire or connection. This determines if PCM and wiring are okay.
- Determines if engine oil temperature signal or sensor ground circuit is open.
Chevrolet Corvette ZR-1 1994 - Diagnostic Aids
If Code 52 was set, engine oil life monitor system has been calculating engine oil life using false information. Oil life monitor must be reset and engine oil and filter changed. A scan tester will read engine oil temperature comparable to MAT or CTS when engine is cold. Temperature reading on tester should rise as engine oil temperature increases. If Code 52 is intermittent, see INTERMITTENTS in TESTS W/O CODES article in this section.
To reset oil life monitor, turn ignition on. Depress and release ENG MET button on trip monitor. Within 5 seconds, depress and release ENG MET button again. Within 5 seconds, depress and hold RANGE button on trip monitor. CHANGE OIL light should flash.
Hold RANGE button until CHANGE OIL light stops flashing. When light goes out, engine oil life monitor is reset. This should take about 10 seconds. If light does not reset, turn ignition off, and repeat procedure.
Chevrolet Corvette ZR-1 1994 - CODE 55, PCM ERROR
Ensure PCM grounds are okay. Ensure correct EPROM is being used and that it is properly installed. If okay, replace PCM. Clear codes, confirm closed loop operation and check operation of Malfunction Indicator Light (MIL).
Chevrolet Corvette ZR-1 1994 - CODE 55, FUEL LEAN MONITOR
PCM is capable of determining if fuel system can deliver adequate fuel during power enrichment (heavy acceleration). During power enrichment conditions, PCM expects to see both O2 sensors registering rich. If both sensors do not register rich, Code 55 will set.
NOTE: Test numbers refer to numbers on diagnostic chart.
- Code 55 will set if PCM detects lean O2 sensor voltage for 8 seconds during power enrichment. This checks for proper fuel pressure.
- Restricting the fuel line allows fuel pressure to build to greater than regulated pressure (greater than 47 psi). DO NOT allow pressure to exceed 60 psi.
Chevrolet Corvette ZR-1 1994 - Diagnostic Aids
A plugged fuel filter or restricted fuel line can prevent adequate fuel from being supplied during power enrichment. Vapor lock can also cause Code 55.
Fig. 63: Chevrolet Corvette ZR-1 1994 - Component Locations - Code 55 Flow Chart
Chevrolet Corvette ZR-1 1994 - CODE 58, TRANSMISSION TEMPERATURE SENSOR HIGH TEMPERATURE
Temperature sensor is a 2 wire thermistor located in transaxle. This sensor operates in the same manner as engine coolant temperature sensor and intake air temperature sensor. PCM applies 5 volts to sensor on signal circuit. Voltage sensed at PCM signal circuit terminal will be high when trans fluid is cold and as fluid warms voltage signal will drop. A very low signal voltage indicates a high fluid temperature or a failure in sensor circuit. Normal fluid temperature range is between 167?F-212?F (75?C-100?C).
Code 58 will set when sensor indicates a temperature of 148?C or greater for 5 seconds. Malfunction Indicator Light (MIL) will illuminate and PCM will use a default sensor value of 90?C.
NOTE: Test numbers refer to numbers on diagnostic chart.
- Checks for a short to ground or an out-of-calibration sensor.
- Checks for an internal fault within the transmission by creating an open.
Chevrolet Corvette ZR-1 1994 - Diagnostic Aids
Check harness routing for a potential short to ground in signal circuit. Temperature should rise steadily to approximately 85?C then stabilize. A skewed sensor could result in delayed shifts or TCC enabled complaints.
Use temperature-to-resistance table to check sensor at various levels to determine if sensor is out-of-calibration, which could result in firm shifts or TCC enable.
Chevrolet Corvette ZR-1 1994 TEMPERATURE-TO-RESISTANCE VALUES (1)
Temperature ?F (?C) Ohms 212 (100) 177 194 (90) 241 158 (70) 467 104 (40) 1459 68 (20) 3520 23 (-5) 12,300 14 (-10) 16,180 0 (-18) 25,000 -4 (-20) 28,680 -22 (-30) 52,700 -40 (-40) 100,700
(1) Measure resistance across sensor terminals.
Chevrolet Corvette ZR-1 1994 - CODE 59, TRANSMISSION TEMPERATURE SENSOR LOW TEMPERATURE
Temperature sensor is a 2 wire thermistor located in transaxle. This sensor operates in the same manner as engine coolant temperature sensor and intake air temperature sensor. PCM applies 5 volts to sensor on signal circuit. Voltage sensed at PCM signal circuit terminal will be high when trans fluid is cold and as fluid warms voltage signal will drop. A very high signal voltage indicates a low fluid temperature or a failure in sensor circuit. Normal fluid temperature range is between 167?F-212?F (75?C-100?C).
Code 59 will set when sensor indicates a temperature of less than -40?C for 5 seconds. Malfunction Indicator Light (MIL) will not illuminate and PCM will use a default sensor value of 90?C.
NOTE: Test numbers refer to numbers on diagnostic chart.
- This test determines if a current condition exists.
- Simulates a Code 58. If PCM recognizes low signal voltage, and scan displays 146 degrees centigrade or higher, PCM and wiring are okay.
- Checks if signal circuit is open. Five volts should be present at sensor connector.
Chevrolet Corvette ZR-1 1994 - Diagnostic Aids
Temperature should rise steadily to approximately 212 ?F (90?C) then stabilize. A faulty connection or an open in ground or signal circuit can result in Code 59. A skewed sensor could result in firm shifts or TCC enabled complaints.
Use temperature-to-resistance table to check sensor at various levels to determine if sensor is out-of-calibration, which could result in firm shifts or TCC enable.
Chevrolet Corvette ZR-1 1994 TEMPERATURE-TO-RESISTANCE VALUES (1)
Temperature ?F (?C) Ohms 212 (100) 177 194 (90) 241 158 (70) 467 104 (40) 1459 68 (20) 3520 23 (-5) 12,300 14 (-10) 16,180 0 (-18) 25,000 -4 (-20) 28,680 -22 (-30) 52,700 -40 (-40) 100,700
(1) Measure resistance across sensor terminals.
Fig. 68: Chevrolet Corvette ZR-1 1994 - Component Locations - Code 59 Flow Chart
Chevrolet Corvette ZR-1 1994 - CODE 61, A/C SYSTEM PERFORMANCE
A/C refrigerant charge is calculated by inputs from the A/C refrigerant pressure and A/C evaporator temperature sensors. PCM will calculate system charge when the A/C is turned on. A/C evaporator temperature and A/C refrigerant temperature 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 and A/C clutch will be disabled; however, SERVICE ENGINE SOON light will not turn on.
NOTE: Test numbers refer to numbers on diagnostic chart.
- Code 61 could be caused by other codes. If other codes exist, use those charts first.
- If the A/C refrigerant pressure sensor is "slewed" (out of calibration), the PCM could be detecting a lower than normal pressure and would set Code 61.
- The conditions to set a Code 67 would cause Code 61 to set. Code 67 will set if the PCM does not detect an A/C refrigerant pressure change of more than 4 psi when the A/C clutch is cycled from off to on.
Chevrolet Corvette ZR-1 1994 - Diagnostic Aids
An out-of-calibration A/C pressure sensor or A/C evaporator temperature sensor could cause Code 61 to set.
Chevrolet Corvette ZR-1 1994 - CODE 62, HIGH ENGINE OIL TEMPERATURE
Engine oil temperature sensor is a thermistor, similar to a coolant or air temperature sensor. When engine oil temperature is cold, sensor resistance is high and PCM will see a high monitored voltage signal on engine oil temperature sensor circuit. As temperature increases, resistance decreases and PCM sees a lower monitored voltage engine oil temperature sensor circuit.
NOTE: Test number refers to number on diagnostic chart.
- Code 62 will set if engine oil temperature sensor indicates a temperature greater than 291?F (144?C) and engine has been running for more than 30 minutes.
Chevrolet Corvette ZR-1 1994 - Diagnostic Aids
If Code 62 was set, engine oil life monitor system has been calculating engine oil life using false information. Oil life monitor must be reset and engine oil and filter changed. Scan tester will read engine oil temperature comparable to MAT or CTS when engine is cold. Temperature reading on tester should rise as engine oil temperature rises. If code is intermittent, see INTERMITTENTS in the TESTS W/O CODES article in this section.
To reset oil life monitor, turn ignition on. Depress and release ENG MET button on trip monitor. Within 5 seconds, depress and release ENG MET button again. Within 5 seconds, depress and hold RANGE button on trip monitor. CHANGE OIL light should flash. Hold RANGE button depressed until CHANGE OIL light stops flashing and goes out. When light goes out, engine oil life monitor is reset. This should take about 10 seconds. If light does not reset, turn ignition off, and repeat procedure.
Chevrolet Corvette ZR-1 1994 - CODE 63, RIGHT OXYGEN SENSOR OPEN
See Code 13 chart and duplicate procedure for right O(2) sensor as necessary.
Chevrolet Corvette ZR-1 1994 - CODE 64, RIGHT OXYGEN (O(2)) SENSOR LEAN
See Code 44 chart and duplicate procedure for right O(2) sensor as necessary.
Chevrolet Corvette ZR-1 1994 - CODE 65, RIGHT OXYGEN (O(2)) SENSOR RICH
See Code 45 chart and duplicate procedure for right O(2) sensor as necessary.
Chevrolet Corvette ZR-1 1994 - CODE 66, A/C PRESSURE SENSOR
A/C pressure sensor responds to changes in A/C refrigerant system high side pressure. PCM uses A/C compressor load input to determine engine idle speed. Sensor uses a 5-volt reference signal from PCM and returns an input signal to PCM 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 PCM.
- 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 PCM.
- 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 Corvette ZR-1 1994 - 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 PCM.
Chevrolet Corvette ZR-1 1994 - CODE 67, A/C PRESSURE SENSOR
PCM determines when A/C clutch is engaged by monitoring A/C status line. If A/C pressure does not increase by at least 4 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 PCM does not detect a A/C pressure change when A/C clutch has been cycled.
- If relay power feed is intermittent, A/C clutch status terminal may not detect voltage when A/C is commanded on.
- Check A/M electrical harness for problems. If A/C clutch status line becomes intermittently open or shorted while compressor is on, PCM will be wrongly detecting A/C clutch going on and off. When this occurs and clutch remains engaged, PCM will not detect pressure change and a Code 67 will be set.
- If A/C compressor clutch status circuit is intermittently open or shorted while compressor is on, PCM will wrongly detect compressor cycling on and off, but PCM will detect no pressure change and a Code 67 will set.
Chevrolet Corvette ZR-1 1994 - Diagnostic Aids
A Code 67 will store in PCM memory but will not turn on the SERVICE ENGINE SOON light. An A/C system low on charge could cause a Code 67 to set.
Chevrolet Corvette ZR-1 1994 - CODE 68, A/C RELAY CIRCUIT SHORTED
When PCM detects A/C has been requested, PCM will activate A/C clutch relay. When relay is activated, voltage should be present at both A/C compressor clutch and A/C clutch status terminal at PCM. If PCM detects voltage on A/C status line when A/C has not been commanded on, Code 68 will set. A short to voltage anywhere on A/C status line, or stuck relay contacts, will set Code 68. When Code 68 is set, PCM does not turn on SERVICE ENGINE SOON light.
NOTE: Test numbers refer to numbers on diagnostic chart.
- Code 68 sets if voltage is detected on A/C status line for more than 20 seconds after PCM has disengaged A/C relay.
- This step will isolate ignition feed portion of circuit from clutch circuit.
- If Code 68 reappears at this step, PCM is internally shorted to voltage.
Chevrolet Corvette ZR-1 1994 - CODE 69, A/C COMPRESSOR RELAY
When PCM detects A/C has been requested, PCM 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 PCM. If the PCM 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 PCM 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 PCM 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 PCM and the splice to the compressor.
Chevrolet Corvette ZR-1 1994 - CODE 70, A/C COMPRESSOR RELAY DRIVER
Relay is supplied voltage when ignition is on. PCM controls solenoid valve by providing a ground through one of its Quad-Drivers Modules (QDM). When relay is actuated, terminal is grounded and its monitored voltage will be low. When an output is off, its terminal voltage will be high. Each QDM has a separate fault line to indicate presence of a current fault to control module central processor.
NOTE: Test numbers refer to numbers on diagnostic chart.
- Tech-1 will enable circuit for 5 seconds.
- This check can detect a partially shorted coil which would cause excessive current flow. Excessive current flow to a QDM will be detected as a fault and set a code.
- The remaining checks will identify a circuit problem that has caused an excessive current flow or inoperative relay.
Chevrolet Corvette ZR-1 1994 - Diagnostic Aids
Check related harness connectors, including PCM harness. Check for damaged or pushed out terminals.
Chevrolet Corvette ZR-1 1994 - CODE 72, VEHICLE SPEED SENSOR LOSS
Speed sensor is a PM generator located on transmission output shaft.
NOTE: Test numbers refer to numbers on diagnostic chart.
- Disable TC system (if equipped) when performing this step. Whenever ignition is cycled to off position and then back to on, TC system will default on.
- An intermittent connection at VSS or PCM may cause code to set. Inspect harness and all related connections. Check for damage or pushed out terminals. Prior to replacing PCM, check for correct software calibration (reprogrammable).
Chevrolet Corvette ZR-1 1994 - Diagnostic Aids
Code 72 will set when vehicle speed has been detected and then lost.
Chevrolet Corvette ZR-1 1994 - CODE 73, PRESSURE CONTROL SOLENOID
Pressure control solenoid is a PCM-controlled device used to regulate transmission line pressure. PCM compares TPS voltage, engine RPM and other inputs to determine proper line pressure for a given load. PCM regulates pressure by applying a varying amperage to pressure control solenoid. Amperage varies from 0.1 to 1.1 amps.
NOTE: Test numbers refer to numbers on diagnostic chart.
- Checks ability of the PCM to command pressure control solenoid.
- Checks for voltage at PCM.
Chevrolet Corvette ZR-1 1994 - Diagnostic Aids
Check for poor connections at PCM and at transmission connector.
Chevrolet Corvette ZR-1 1994 - CODE 74, TRACTION CONTROL VOLTAGE LOW
PCM monitors traction control system activity (battery voltage input signal) and inhibit upshifts, downshifts and TCC operation during system activity (zero volts on signal line).
NOTE: Test numbers refer to numbers on diagnostic chart.
- If fault exists, scan tester will display TCS activity. A short to ground in an external component or wiring could be the cause for setting of code.
Chevrolet Corvette ZR-1 1994 - Diagnostic Aids
Check related harness connectors, including PCM harness. Check for damaged or pushed out terminals. Wiggle harness while monitoring scan tester TCS status. If status changes, wiring is faulty.
Chevrolet Corvette ZR-1 1994 - CODE 75, TRANSMISSION VOLTAGE LOW
NOTE: Test numbers refer to numbers on diagnostic chart.
- Checks for normal battery voltage of 9-15 volts.
- Checks if low voltage is due to generator voltage supply circuit, or PCM. If voltage is less than 9 volts, PCM is okay.
Chevrolet Corvette ZR-1 1994 - Diagnostic Aids
If code sets when an accessory is operated, check for poor connections or excessive current draw. Also, check for poor connections at starter solenoid or fusible link.
Chevrolet Corvette ZR-1 1994 - CODE 77, PRIMARY COOLING FAN DRIVER
Cooling fan relay is supplied voltage when ignition is on. PCM controls solenoid valve by providing a ground through one of its Quad-Drivers Modules (QDM). When relay is actuated, terminal is grounded and its monitored voltage will be low. When an output is off, its terminal voltage will be high. Each QDM has a separate fault line to indicate presence of a current fault to control module central processor.
NOTE: Test numbers refer to numbers on diagnostic chart.
- Tech-1 will enable circuit for 5 seconds.
- This check can detect a partially shorted coil which would cause excessive current flow. Excessive current flow to a QDM will be detected as a fault and set a code.
- The remaining checks will identify a circuit problem that has caused an excessive current flow or inoperative relay.
Chevrolet Corvette ZR-1 1994 - Diagnostic Aids
Check related harness connectors, including PCM harness. Check for damaged or pushed out terminals.
Fig. 92: Chevrolet Corvette ZR-1 1994 - Component Locations - Code 77 Flow Chart
Chevrolet Corvette ZR-1 1994 - CODE 78, SECONDARY COOLING FAN DRIVER
Cooling fan relay is supplied voltage when ignition is on. PCM controls solenoid valve by providing a ground through one of its Quad-Drivers Modules (QDM). When relay is actuated, terminal is grounded and its monitored voltage will be low. When an output is off, its terminal voltage will be high. Each QDM has a separate fault line to indicate presence of a current fault to control module central processor.
NOTE: Test numbers refer to numbers on diagnostic chart.
- Tech-1 will enable circuit for 5 seconds.
- This check can detect a partially shorted coil which would cause excessive current flow. Excessive current flow to a QDM will be detected as a fault and set a code.
- The remaining checks will identify a circuit problem that has caused an excessive current flow or inoperative relay.
Chevrolet Corvette ZR-1 1994 - Diagnostic Aids
Check related harness connectors, including PCM harness. Check for damaged or pushed out terminals.
Chevrolet Corvette ZR-1 1994 - CODE 79, TRANSMISSION FLUID OVERTEMP
PCM supplies and monitors a 5-volt reference to sensor. As transmission temperature changes, sensor resistance changes, affecting monitored voltage. When fluid is cold, resistance is high, resulting in a high monitored voltage.When fluid is hot, resistance is low, resulting in a low monitored voltage.
NOTE: Test numbers refer to numbers on diagnostic chart.
- Checks for out-of-calibration sensor or shorted circuit.
- Simulates Code 59.
Chevrolet Corvette ZR-1 1994 - Diagnostic Aids
See Code 59 chart to check transmission temperature sensor temperature-to-resistance values. Also, check transmission fluid level.
Chevrolet Corvette ZR-1 1994 TEMPERATURE-TO-RESISTANCE VALUES (1)
Temperature ?F (?C) Ohms 212 (100) 177 194 (90) 241 158 (70) 467 104 (40) 1459 68 (20) 3520 23 (-5) 12,300 14 (-10) 16,180 0 (-18) 25,000 -4 (-20) 28,680 -22 (-30) 52,700 -40 (-40) 100,700
(1) Measure resistance across sensor terminals.
Chevrolet Corvette ZR-1 1994 - CODE 80, TRANSMISSION COMPONENT SLIPPING
PCM monitors difference between engine speed and transmission input shaft speed. With selector in D3 or D4 (indicated gear 2, 3 or 4), and TCC is locked, scan should display engine speed closely matching input speed.
NOTE: Test numbers refer to numbers on diagnostic chart.
- Checks indicated range signal to the actual selected range.
- Checks torque converter for slippage while in a commanded locked-up state.
Chevrolet Corvette ZR-1 1994 - Diagnostic Aids
Check for poor connections at pass-through connector. A faulty transmission range pressure switch assembly may set Code 80.
Chevrolet Corvette ZR-1 1994 - CODE 81, 2-3 SHIFT SOLENOID
Voltage is supplied directly to solenoid. PCM controls solenoid by providing a ground circuit.
NOTE: Test numbers refer to numbers on diagnostic chart.
- Checks 2-3 shift solenoid and internal transmission for shorts.
- Checks for power to 2-3 shift solenoid from ignition through the fuse.
Chevrolet Corvette ZR-1 1994 - Diagnostic Aids
Check all connections at the transmission. An open in ignition feed circuit can cause multiple codes to set.
Chevrolet Corvette ZR-1 1994 - CODE 82, 1-2 SHIFT SOLENOID
Voltage is supplied directly to solenoid. PCM controls solenoid by providing a ground circuit for solenoid.
NOTE: Test numbers refer to numbers on diagnostic chart.
- Checks 1-2 shift solenoid and internal transmission for shorts.
- Checks for power to 1-2 shift solenoid from ignition through the fuse.
Chevrolet Corvette ZR-1 1994 - Diagnostic Aids
Check all connections at the transmission. An open in ignition feed circuit can cause multiple codes to set.
Chevrolet Corvette ZR-1 1994 - CODE 84, 3-2 CONTROL SOLENOID - A/T
NOTE: Test numbers refer to numbers on diagnostic chart.
- Checks 3-2 shift solenoid and internal transmission for shorts.
- Checks for power to 3-2 shift solenoid from ignition through the fuse.
Chevrolet Corvette ZR-1 1994 - Diagnostic Aids
Check all connections at the transmission. An open in ignition feed circuit can cause multiple codes to set.
Fig. 105: Chevrolet Corvette ZR-1 1994 - Component Locations - Code 84 Flow Chart
Chevrolet Corvette ZR-1 1994 - CODE 84, 2ND TO 3RD GEAR BLOCKOUT RELAY - M/T
Ignition voltage is supplied to 2nd and 3rd gear blockout relay. PCM controls relay by providing a ground during certain light load operating conditions. Relay in turn energizes solenoid on transmission. When solenoid is enabled, transmission can be shifted from 1st to 4th gear only. This maximizes fuel economy.
NOTE: Test numbers refer to numbers on diagnostic chart.
- Tech-1 will energize circuit for 5 seconds. 2 Detects a partially shorted coil which would cause excessive current flow. Leave circuit energized for 2 minutes to allow coil to warm. Coil may then open, causing amperage to drop to zero.
Chevrolet Corvette ZR-1 1994 - Diagnostic Aids
Inspect harness and all related connections, including PCM connections. These may cause an intermittent code to set.
Chevrolet Corvette ZR-1 1994 - CODE 85, TCC STUCK ON
NOTE: Test numbers refer to numbers on diagnostic chart.
- Checks mechanical state of TCC when PCM commands TCC solenoid off. TCC slip speed should increase.
Chevrolet Corvette ZR-1 1994 - Diagnostic Aids
If TCC is mechanically stuck on, vehicle speed is zero, brakes are applied, and D2 is selected, TCC fluid will mechanically apply the TCC, causing an engine stall.
Chevrolet Corvette ZR-1 1994 - CODE 90, TCC SOLENOID CIRCUIT
NOTE: Test numbers refer to numbers on diagnostic chart.
- Checks for a shorted internal transmission harness or TCC solenoid.
- Checks power supply to TCC solenoid.
Chevrolet Corvette ZR-1 1994 - Diagnostic Aids
Check all connections to transmission pass-through connector. An open in the ignition feed circuit will cause multiple codes to set.
Chevrolet Corvette ZR-1 1994 - CODE 91, 1-4 UPSHIFT LIGHT
When 1-4 shift light is energized, PCM is energizing 2nd-3rd blockout relay and gearshift can only be moved from 1st to 4th gear. This will occur only once per upshift cycle. Upshift can not be repeated until vehicle speed drops to less than one MPH.
NOTE: Test numbers refer to numbers on diagnostic chart.
- The 1-4 upshift light should not turn on. If light is on, circuit is shorted to ground or PCM is faulty.
- PCM should turn on 1-4 upshift light.
- Checks 1-4 upshift light circuit up to the PCM connector. If light illuminates, PCM connector is faulty or PCM does not have the ability to ground circuit.
Chevrolet Corvette ZR-1 1994 - Diagnostic Aids
Inspect harness and all related connections, including PCM connections. These may cause an intermittent code to set.
Chevrolet Corvette ZR-1 1994 - CODE 97, VSS OUTPUT CIRCUIT
NOTE: Test numbers refer to numbers on diagnostic chart.
- Disable Traction Control (TC) system (if equipped) prior to this step. Switch is located in glove box. Whenever ignition is cycled off and then on, TC system will default to on. If vehicle speed is indicated at this point, code is intermittent.
- Use Jumper Harness (J 35616-A) to prevent damage to harness.
Chevrolet Corvette ZR-1 1994 - Diagnostic Aids
Inspect harness and all related connections, including PCM connections.
Chevrolet Corvette ZR-1 1994 - CODE P0116, ECT SENSOR CIRCUIT RANGE/PERFORMANCE PROBLEM
While engine is warming, PCM monitors Engine Coolant Temperature (ECT) sensor to determine the amount of time is required for the engine to reach the coolant temperature required for closed loop operation. Code P0116 will set if PCM determines that engine does not reach closed loop operation temperature in a specified amount of time. This test will not be run if either intake air or engine coolant temperatures are less than -13?F (-25?C). PCM will only run P0116 only on a cold start, and only once per cold start.
Code P0116 will set when the following conditions are present.
- Engine coolant and intake air temperatures are greater than -13?F(-25?C), but less than 90?F (50?C) at start-up.
- Engine coolant and intake air temperatures are not more than 11?F (6?C) different at start-up.
- Codes 23, 25, P0117 and P0118 are not set.
- Closed loop temperature of 138?F (59?C) is not obtained within 22 minutes.
Code P0116 will be stored in PCM memory, but will not illuminate Malfunction Indicator Light (MIL). A failed last test code will clear when the fault conditions no longer exist. A history code will clear after 40 ignition cycles without a fault, when the battery has been disconnected for 30 seconds, or when the code clearing feature on the Tech-1 is used.
NOTE: Test numbers refer to numbers on diagnostic chart.
- An ECT failure may cause Code P0116 to set. Correct an codes that are set. PCM will only run Code P0116 when engine coolant and intake air temperatures are greater than -13?F (-25?C), but less than 90?F (50?C).
- This test determines if PCM and circuit 410 (Yellow wire) are okay. High resistance in circuit 410 (Yellow wire) will cause engine coolant temperature to be at a fixed value, causing Code P0116 to set.
- A faulty thermostat or coolant system problem could cause engine to warm slowly. Diagnose coolant system malfunction. Check cooling fan operation.
Chevrolet Corvette ZR-1 1994 - Diagnostic Aids
An ECT sensor that is skewed/fixed at a temperature less than 138?F (59?C) will cause Code P0116 to set.
To verify repair, vehicle must be below start-up coolant temperature for the PCM to run test. Using Tech-1, select OBD-II test status, start engine and idle. Monitor OBD-II test status for Code P0116 and determine if test runs and passes.
Chevrolet Corvette ZR-1 1994 TEMPERATURE-TO-RESISTANCE VALUES (1)
Temperature ?F (?C) Ohms 212 (100) 177 194 (90) 241 158 (70) 467 104 (40) 1459 68 (20) 3520 23 (-5) 12,300 14 (-10) 16,180 0 (-18) 25,000 -4 (-20) 28,680 -22 (-30) 52,700 -40 (-40) 100,700
(1) Measure resistance across sensor terminals.
Chevrolet Corvette ZR-1 1994 - CODE P0117, COOLANT TEMP SENSOR LOW TEMP INDICATED
ECT sensor uses a thermistor to control signal voltage to PCM. PCM applies and monitors a 5 volts to ECT sensor. When engine coolant is cold, sensor (thermistor) resistance is high and PCM will sense a high signal voltage. As engine coolant warms up, sensor resistance becomes less and PCM voltage drops. With Code P0117 set, PCM will turn cooling fans on and use a default engine coolant temperature value based on run time. PCM will illuminate Malfunction Indicator Light (MIL).
NOTE: Test numbers refer to numbers on diagnostic chart.
- Code 14 reference applies to Corvette only. This step determines if conditions necessary to set Code P0117 exist.
- Determines if circuit is shorted to ground.
Chevrolet Corvette ZR-1 1994 - Diagnostic Aids
Tech 1 displays engine temperature in degrees Celsius (?C) and Fahrenheit (?F). After engine is started, temperature should rise steadily to 194?F (90?C), then stabilize when thermostat opens. An intermittent may be caused by a poor connection, rubbed through wire insulation or a wire broken inside the insulation. Check for:
- Poor Connection Or Damaged Harness: Inspect PCM harness connectors for backed out terminals, improper mating, broken locks, improperly formed or damaged terminals, poor terminal to wire connection, and damaged harness.
- Intermittent Test: Using Tech 1, monitor engine coolant temperature while moving related connectors and wiring harness. If failure is induced, display will change. This may assist in isolating the location of the malfunction.
- Shifted Sensor: See TEMPERATURE-TO-RESISTANCE VALUES table to test ECT sensor at various temperature levels to evaluate the possibility of a shifted (mis-scaled) sensor which may result in driveability complaints.
- A faulty connection, or an open in sensor circuits will cause Code P0117 to set.
Chevrolet Corvette ZR-1 1994 TEMPERATURE-TO-RESISTANCE VALUES (1)
Temperature ?F (?C) Ohms 212 (100) 177 194 (90) 241 158 (70) 467 104 (40) 1459 68 (20) 3520 23 (-5) 12,300 14 (-10) 16,180 0 (-18) 25,000 -4 (-20) 28,680 -22 (-30) 52,700 -40 (-40) 100,700
(1) Measure resistance across sensor terminals.
Chevrolet Corvette ZR-1 1994 - CODE P0118, COOLANT TEMP SENSOR HIGH TEMP INDICATED
ECT sensor uses a thermistor to control signal voltage to PCM. PCM applies and monitors a 5 volts to ECT sensor. When engine coolant is cold, sensor (thermistor) resistance is high and PCM will sense a high signal voltage. As engine coolant warms up, sensor resistance becomes less and PCM voltage drops. With Code P0118 set, PCM will turn cooling fans on and use a default engine coolant temperature value based on run time. PCM will illuminate Malfunction Indicator Light (MIL).
NOTE: Test numbers refer to numbers on diagnostic chart.
- Code 15 reference applies to Corvette only. This step determines if conditions necessary to set Code P0118 exist.
- This test will determine if signal circuit is shorted to ground which will cause conditions for Code P0118.
- This test will determine if circuit is open. If circuits are okay, check connections at PCM and ECT sensor.
Chevrolet Corvette ZR-1 1994 - Diagnostic Aids
Tech 1 displays engine temperature in degrees Celsius (?C) and Fahrenheit (?F). After engine is started, temperature should rise steadily to 194?F (90?C), then stabilize when thermostat opens. An intermittent may be caused by a poor connection, rubbed through wire insulation or a wire broken inside the insulation. Check the following for:
- A short to ground in circuit No. 410 (Yellow wire).
- Intermittent Test: Using Tech 1, monitor engine coolant temperature while moving related connectors and wiring harness. If failure is induced, display will change. This may assist in isolating the location of the malfunction.
- Shifted Sensor: See TEMPERATURE-TO-RESISTANCE VALUES table to test ECT sensor at various temperature levels to evaluate the possibility of a shifted (mis-scaled) sensor which may result in driveability complaints.
Chevrolet Corvette ZR-1 1994 TEMPERATURE-TO-RESISTANCE VALUES (1)
Temperature ?F (?C) Ohms 212 (100) 177 194 (90) 241 158 (70) 467 104 (40) 1459 68 (20) 3520 23 (-5) 12,300 14 (-10) 16,180 0 (-18) 25,000 -4 (-20) 28,680 -22 (-30) 52,700 -40 (-40) 100,700
(1) Measure resistance across sensor terminals.
Chevrolet Corvette ZR-1 1994 - CODE P0131, BANK 1 O2 SENSOR NO. 1 LOW VOLTAGE SIGNAL (LEAN)
PCM continuously monitors and stores Heated Oxygen Sensor (HO2S) voltage information. PCM evaluates HO2S voltage samples every 100 seconds to determine the amount of time the HO2S voltage was indicating a rich, lean or an inactive condition. PCM will compare the stored HO2S voltage samples taken within each 100 second sample period and determine statistically if a majority of the samples were above or below a predetermined threshold. PCM can also determine if HO2S voltage is indicating an inactive signal. The inactive signal would spend a majority of the time near the HO2S bias voltage. Code P0131 will set when the following conditions are present.
- Engine is operating in closed loop mode.
- TP sensor angle is between 2 and 10 percent.
- Codes 14, 15, 18, 21, 22, 24, 26, 29, 33, 34, 36, 43, 47, 48, 50, 51, 53, 55, P0116, P0117, P0118, P0171, P0172, P0174, P0175, P1114 and P1115 are not set.
- Majority of HO2S voltage samples are less than .141 volt.
- All conditions are met for 102 seconds.
- A failed last test code will occur on the first fault.
- A history code will occur on the second drive cycle with a fault.
Code P0131 will be stored in PCM memory, but will not illuminate Malfunction Indicator Light (MIL). A failed last test code will clear when the fault conditions no longer exist. A history code will clear after 40 ignition cycles without a fault, when the battery has been disconnected for 30 seconds, or when the code clearing feature on the Tech 1 is used.
NOTE: Engine must be at normal operating temperature before performing this test.
Chevrolet Corvette ZR-1 1994 - Diagnostic Aids
Using Tech 1, observe long term fuel trim values at different RPM and air flow conditions. Tech 1 also displays fuel trim cells, allowing the long term fuel trim values to be checked in each of the cells, thus determining when Code P0131 may have been set. If the conditions for Code P0131 exist, the long term fuel trim values will be near 160.
Check for mispositioned HO2S pigtail or for pigtail that may be contacting the exhaust manifold. Check HO2S connections and wire for breakage or contamination that could prevent reference oxygen from reaching HO2S. Check for intermittent ground in signal wire between connector and sensor. Check for lean injectors. Check for water near in-tank fuel pump inlet causing fuel contamination in fuel delivered to injectors. Check for low fuel pressure. Check for an exhaust leak above the oxygen sensor allowing outside air to be pulled into exhaust stream and flow past sensor. Check for vacuum or crankcase leaks. Ensure the secondary air pump is not operating in closed loop. If all checks are okay, oxygen sensor may be faulty.
Chevrolet Corvette ZR-1 1994 - CODE P0132, BANK 1 O2 SENSOR NO. 1 HIGH SIGNAL VOLTAGE (RICH)
PCM continuously monitors and stores Heated Oxygen Sensor (HO2S) voltage information. PCM evaluates HO2S voltage samples every 100 seconds to determine the amount of time the HO2S voltage was indicating a rich, lean or an inactive condition. PCM will compare the stored HO2S voltage samples taken within each 100 second sample period and determine statistically if a majority of the samples were above or below a predetermined threshold. PCM can also determine if HO2S voltage is indicating an inactive signal. The inactive signal would spend a majority of the time near the HO2S bias voltage. Code P0132 will set when the following conditions are present.
- Engine is operating in closed loop mode.
- TP sensor angle is between 2 and 10 percent.
- Codes 14, 15, 18, 21, 22, 24, 26, 29, 33, 34, 36, 43, 47, 48, 50, 51, 53, 55, P0116, P0117, P0118, P0171, P0172, P0174, P0175, P1114 and P1115 are not set.
- Majority of HO2S voltage samples are greater than .85 volt.
- All conditions are met for 102 seconds.
- A failed last test code will occur on the first fault.
- A history code will occur on the second drive cycle with a fault.
Code P0132 will be stored in PCM memory, but will not illuminate Malfunction Indicator Light (MIL). A failed last test code will clear when the fault conditions no longer exist. A history code will clear after 40 ignition cycles without a fault, when the battery has been disconnected for 30 seconds, or when the code clearing feature on the Tech 1 is used.
NOTE: Engine must be at normal operating temperature before performing this test.
Chevrolet Corvette ZR-1 1994 - Diagnostic Aids
Using Tech 1, observe long term fuel trim values at different RPM and load conditions. Tech 1 also displays fuel trim cells, allowing the long term fuel trim values to be checked in each of the cells, thus determining when Code P0132 may have been set. If the conditions for Code P0132 exist, the long term fuel trim values will be near 108.
Check for high fuel pressure. Check for rich injectors. Check for leaking injectors. Check evaporative emission (EVAP) canister purge for fuel saturation. If full of fuel, check canister control and hoses. Disconnect MAF sensor and check if rich condition is corrected. If rich condition is corrected, check MAF sensor of proper installation. If installation is okay, replace MAF sensor. Check for leaking fuel pressure regulator diaphragm. Check TP sensor output. Check for a stuck open EGR valve (especially at idle). Check HO2S connections and wire for breakage or contamination that could prevent reference oxygen from reaching HO2S.
Chevrolet Corvette ZR-1 1994 - CODE P0133, BANK 1 HO2S NO. 1 CIRCUIT SLOW RESPONSE
PCM continuously monitors Heated Oxygen Sensor (HO2S) activity for 100 seconds. During the monitoring, the PCM counts the number of times the HO2S switches from rich to lean and from lean to rich, and adds the amount of time required to complete all switches. Thus, an average time for all switches can be determined. If the average time to switch is too slow, Code P0133 will set. A HO2S that switches too slowly is most likely defective and should be replaced. Code P0133 will set when the following conditions are present.
- Engine is started.
- Intake air and engine coolant temperatures are less than 122?F (50?C).
- Intake air and engine coolant temperatures are within 11?F (6?C) of one another at start-up.
- TP sensor angle is between 2 and 10 percent for 100 seconds.
- Engine is operating in closed loop mode.
- Codes 14, 15, 18, 21, 22, 24, 26, 29, 33, 34, 36, 43, 47, 48, 50, 51, 53, 55, P0116, P0117, P0118, P0171, P0172, P0174, P0175, P1114 and P1115 are not set.
- All conditions are met, and the average time for the HO2S to switch from lean to rich is longer than .1 second, or the average time for the HO2S to switch from rich to lean is longer than .1 second.
A lean to rich switch is determined when the HO2S voltage changes from less than .3 volt to greater than .6 volt. A rich to lean switch is determined when the HO2S voltage changes from greater than .6 volt to less than .3 volt. Code P0133 will only fail on a cold start with ECT and IAT less than 122?F (50?C), and within 11?F (6?C) at start-up. If a condition for Code P0133 is present and ECT is greater than 122?F (50?C), PCM will not run Code P0133 test.
Code P0133 will be stored in PCM memory, but will not illuminate Malfunction Indicator Light (MIL). A failed last test code will clear when the fault conditions no longer exist. A history code will clear after 40 ignition cycles without a fault, when the battery has been disconnected for 30 seconds, or when the code clearing feature on the Tech 1 is used.
NOTE: Test numbers refer to numbers on diagnostic chart.
- Code P0135 (HO2S HEATER CIRCUIT MALFUNCTION) can cause Code P0133 to set. Repair heater circuit before proceeding with this chart.
- An exhaust leak 6-12" away from HO2S in either direction can cause Code P0133 to set. Thoroughly inspect exhaust system for leaks.
- An HO2S that is contaminated by oil will be Dark Brown in appearance. An HO2S that is contaminated by coolant will be Whitish Green in appearance.
- Certain RTV silicone gasket materials release vapors that can contaminate the HO2S. Silicone in the fuel can cause silica contamination. If sensor appears to be contaminated by silica, and all other sealants are non-silica base, advise customer to select a different fuel company. A missing fuel filler restrictor indicates leaded fuel may have been used.
Chevrolet Corvette ZR-1 1994 - Diagnostic Aids
To verify repair or to determine if condition is intermittent, monitor OBD-II test status for Code P0133.
Chevrolet Corvette ZR-1 1994 - CODE P0134, BANK 1 OXYGEN SENSOR NO. 1 NO ACTIVITY DETECTED
PCM continuously monitors and stores Heated Oxygen Sensor (HO2S) voltage information. PCM evaluates HO2S voltage samples every 100 seconds to determine the amount of time the HO2S voltage was indicating a rich, lean or an inactive condition. PCM will compare the stored HO2S voltage samples taken within each 100 second sample period and determine statistically if a majority of the samples were above or below a predetermined threshold. PCM can also determine if HO2S voltage is indicating an inactive signal. The inactive signal would spend a majority of the time near the HO2S bias voltage. Code P0134 will set when the following conditions are present.
- Engine is operating in closed loop mode.
- TP sensor angle is between 2 and 10 percent.
- Codes 14, 15, 18, 21, 22, 24, 26, 29, 33, 34, 36, 43, 47, 48, 50, 51, 53, 55, P0116, P0117, P0118, P0171, P0172, P0174, P0175, P1114 and P1115 are not set.
- Majority of HO2S voltage samples are between .35-.50 volt.
- All conditions are met for 102 seconds.
- A failed last test code will occur on the first fault.
- A history code will occur on the second drive cycle with a fault.
Code P0134 will be stored in PCM memory, but will not illuminate Malfunction Indicator Light (MIL). A failed last test code will clear when the fault conditions no longer exist. A history code will clear after 40 ignition cycles without a fault, when the battery has been disconnected for 30 seconds, or when the code clearing feature on the Tech 1 is used.
NOTE: Test numbers refer to numbers on diagnostic chart.
- The OBD-II test status for Code P0134 will be displayed on Tech 1. If the PCM runs the test for Code P0134 and passes, Tech 1 will indicate YES in the RAN column and YES in the PASS column. If PCM fails the test, Tech 1 will indicate YES in RAN column and NO in PASS column. When PCM detects that the test passed then failed, Tech 1 will indicate YES in RAN column and INT (intermittent) in PASS column. If OBD-II test status does not change in the RAN column, ensure all criteria is met that is required to set Code P0134. Engine must be at normal operating temperature before proceeding with this test. This procedure will require a minimum of 3 minutes to run.
- Jumpering circuits to ground should cause HO2S voltage to become less than .2 volt. With circuits shorted to ground, move related HO2S and PCM harnesses while monitoring HO2S voltage on Tech 1. If voltage increases from less than .20 volt to approximately .45 volt, inspect all connections and wiring for intermittent opens.
- Use only a high impedance DVOM for this test.
- Thoroughly inspect all connections and wiring. If connections and wiring are okay, replace bank 1 HO2S No. 1.
Chevrolet Corvette ZR-1 1994 - Diagnostic Aids
An OBD-II test status that indicates INT means the PCM has failed and passed the test during this ignition cycle.
Chevrolet Corvette ZR-1 1994 - CODE P0135, BANK 1 O2 SENSOR NO. 1 HEATER CIRCUIT MALFUNCTION
PCM supplies a bias voltage (approximately .45 volt) on the Heated Oxygen Sensor (HO2S) signal high and low circuits. Battery voltage is supplied to HO2S heater when ignition is turned on. HO2S voltage changes from a bias voltage range to normal operation as HO2S heater reaches operating temperature. HO2S voltage on a cold engine, typically, changes from a bias voltage to a voltage less than .30 volt as HO2S reaches operating temperature. HO2S voltage could possibly increase to greater than .45 volt depending upon the exhaust gas content.
PCM will run heater test only on a cold start (dependent upon coolant and intake air temperatures) and only once per ignition cycle. PCM will monitor HO2S voltage when engine is started. PCM will determine how much time elapsed when HO2S voltage increases above or decreases below the bias range threshold.
Code P0135 will set if the PCM detects too much time elapsed for the HO2S to enter normal operating range. The time required for HO2S to reach operating temperature is based off of engine coolant temperature. If engine coolant temperature is -40?F (-40?C), HO2S should reach operating temperature within 200 seconds. If engine coolant temperature is 154?F (68?C), HO2S should reach operating temperature within 48 seconds. Code P0135 will set when the following conditions are present.
- Engine is started.
- Intake air and engine coolant temperatures are less than 122?F (50?C).
- Intake air and engine coolant temperatures are within 11?F (6?C) of one another at start-up.
- TP sensor angle is less than 16 percent.
- HO2S voltage remains between .3-.7 volt for more than 200 seconds if engine coolant temperature is -40?F (-40?C), or 48 seconds when engine coolant temperature is greater than 154?F (68?C).
Code P0135 will be stored in PCM memory, but will not illuminate Malfunction Indicator Light (MIL). A failed last test code will clear when the fault conditions no longer exist. A history code will clear after 40 ignition cycles without a fault, when the battery has been disconnected for 30 seconds, or when the code clearing feature on the Tech 1 is used.
NOTE: Test numbers refer to numbers on diagnostic chart.
- If Codes P0155 and P0161 are also set, the ignition feed circuit to heated oxygen sensors may be open. Check oxygen sensor fuse located in instrument panel fuse block. HO2S voltage should change from a bias voltage to less than .3 volt or greater than .7 volt within 48 seconds if engine coolant temperature is greater than 154?F (68?C), or within 200 seconds if engine coolant temperature is -40?F (-40?C).
- A contaminated HO2S should be replaced and the condition causing contamination repaired (silicone, lead, engine oil and coolant, etc.).
Chevrolet Corvette ZR-1 1994 - Diagnostic Aids
Engine must be below the start-up coolant temperature for the PCM to run Code P0135 test. To verify repair or to determine if condition is intermittent, monitor OBD-II test status for Code P0135.
Chevrolet Corvette ZR-1 1994 - CODE P0151, BANK 2 O2 SENSOR NO. 1 LOW SIGNAL VOLTAGE (LEAN)
PCM continuously monitors and stores Heated Oxygen Sensor (HO2S) voltage information. PCM evaluates HO2S voltage samples every 100 seconds to determine the amount of time the HO2S voltage was indicating a rich, lean or an inactive condition. PCM will compare the stored HO2S voltage samples taken within each 100 second sample period and determine statistically if a majority of the samples were above or below a predetermined threshold. PCM can also determine if HO2S voltage is indicating an inactive signal. The inactive signal would spend a majority of the time near the HO2S bias voltage. Code P0151 will set when the following conditions are present.
- Engine is operating in closed loop mode.
- TP sensor angle is between 2 and 10 percent.
- Codes 14, 15, 18, 21, 22, 24, 26, 29, 33, 34, 36, 43, 47, 48, 50, 51, 53, 55, P0116, P0117, P0118, P0171, P0172, P0174, P0175, P1114 and P1115 are not set.
- Majority of HO2S voltage samples are less than .14 volt.
- All conditions are met for 102 seconds.
- A failed last test code will occur on the first fault.
- A history code will occur on the second drive cycle with a fault.
Code P0151 will be stored in PCM memory, but will not illuminate Malfunction Indicator Light (MIL). A failed last test code will clear when the fault conditions no longer exist. A history code will clear after 40 ignition cycles without a fault, when the battery has been disconnected for 30 seconds, or when the code clearing feature on the Tech 1 is used.
NOTE: Ensure engine is at normal operating temperature before performing this test.
Chevrolet Corvette ZR-1 1994 - Diagnostic Aids
Using Tech 1, observe long term fuel trim values at different RPM and airflow conditions. Tech 1 also displays fuel trim cells, allowing the long term fuel trim values to be checked in each of the cells, thus determining when Code P0151 may have been set. If the conditions for Code P0151 exist, the long term fuel trim values will be near 160.
Check for mispositioned HO2S pigtail or for pigtail that may be contacting the exhaust manifold. Check HO2S connections and wire for breakage or contamination that could prevent reference oxygen from reaching HO2S. Check for intermittent ground in signal wire between connector and sensor. Check for lean injectors. Check for water near in-tank fuel pump inlet causing fuel contamination in fuel delivered to injectors. Check for low fuel pressure. Check for an exhaust leak above the oxygen sensor allowing outside air to be pulled into exhaust stream and flow past sensor. Check for vacuum or crankcase leaks. Ensure the secondary air pump is not operating in closed loop. If all of the above checks are okay, the oxygen sensor may be faulty.
Chevrolet Corvette ZR-1 1994 - CODE P0152, BANK 2 O2 SENSOR NO. 1 HIGH SIGNAL VOLTAGE (RICH)
PCM continuously monitors and stores Heated Oxygen Sensor (HO2S) voltage information. PCM evaluates HO2S voltage samples every 100 seconds to determine the amount of time the HO2S voltage was indicating a rich, lean or an inactive condition. PCM will compare the stored HO2S voltage samples taken within each 100 second sample period and determine statistically if a majority of the samples were above or below a predetermined threshold. PCM can also determine if HO2S voltage is indicating an inactive signal. The inactive signal would spend a majority of the time near the HO2S bias voltage. Code P0152 will set when the following conditions are present.
- Engine is operating in closed loop mode.
- TP sensor angle is between 2 and 10 percent.
- Codes 14, 15, 18, 21, 22, 24, 26, 29, 33, 34, 36, 43, 47, 48, 50, 51, 53, 55, P0116, P0117, P0118, P0171, P0172, P0174, P0175, P1114 and P1115 are not set.
- Majority of HO2S voltage samples are greater than .85 volt.
- All conditions are met for 102 seconds.
- A failed last test code will occur on the first fault.
- A history code will occur on the second drive cycle with a fault.
Code P0152 will be stored in PCM memory, but will not illuminate Malfunction Indicator Light (MIL). A failed last test code will clear when the fault conditions no longer exist. A history code will clear after 40 ignition cycles without a fault, when the battery has been disconnected for 30 seconds, or when the code clearing feature on the Tech 1 is used.
NOTE: Ensure engine is at normal operating temperature before performing this test.
Chevrolet Corvette ZR-1 1994 - Diagnostic Aids
Using Tech 1, observe long term fuel trim values at different RPM and load conditions. Tech 1 also displays fuel trim cells, allowing the long term fuel trim values to be checked in each of the cells, thus determining when Code P0152 may have been set. If the conditions for Code P0152 exist, the long term fuel trim values will be near 108.
Check for high fuel pressure. Check for rich injectors. Check for leaking injectors. Check evaporative emission (EVAP) canister purge for fuel saturation. If full of fuel, check canister control and hoses. Disconnect MAF sensor and check if rich condition is corrected. If rich condition is corrected, check MAF sensor of proper installation. If installation is okay, replace MAF sensor. Check for leaking fuel pressure regulator diaphragm. Check TP sensor output. Check for a stuck open EGR valve (especially at idle). Check HO2S connections and wire for breakage or contamination that could prevent reference oxygen from reaching HO2S.
Chevrolet Corvette ZR-1 1994 - CODE P0153, BANK 2 OXYGEN SENSOR NO. 1 SLOW RESPONSE
PCM continuously monitors Heated Oxygen Sensor (HO2S) activity for 100 seconds. During the monitoring, the PCM counts the number of times the HO2S switches from rich to lean and from lean to rich, and adds the amount of time required to complete all switches. Thus, an average time for all switches can be determined. If the average time to switch is too slow, Code P0153 will set. A HO2S that switches too slowly is most likely defective and should be replaced.
Code P0153 will set when the following conditions are present.
- Engine is started.
- Intake air and engine coolant temperatures are less than 122?F (50?C).
- Intake air and engine coolant temperatures are within 11?F (6?C) of one another at start-up.
- TP sensor angle is between 2 and 10 percent for 100 seconds.
- Engine is operating in closed loop mode.
- Codes 14, 15, 18, 21, 22, 24, 26, 29, 33, 34, 36, 43, 47, 48, 50, 51, 53, 55, P0116, P0117, P0118, P0171, P0172, P0174, P0175, P1114 and P1115 are not set.
- All conditions are met, and the average time for the HO2S to switch from lean to rich is longer than .1 second, or the average time for the HO2S to switch from rich to lean is longer than .1 second.
A lean to rich switch is determined when the HO2S voltage changes from less than .3 volt to greater than .6 volt. A rich to lean switch is determined when the HO2S voltage changes from greater than .6 volt to less than .3 volt. Code P0153 will only fail on a cold start with ECT and IAT less than 122?F (50?C), and within 11?F (6?C) at start-up. If a condition for Code P0153 is present and ECT is greater than 122?F (50?C), PCM will not run Code P0153 test.
Code P0153 will be stored in PCM memory, but will not illuminate Malfunction Indicator Light (MIL). A failed last test code will clear when the fault conditions no longer exist. A history code will clear after 40 ignition cycles without a fault, when the battery has been disconnected for 30 seconds, or when the code clearing feature on the Tech 1 is used.
NOTE: Test numbers refer to numbers on diagnostic chart.
- Code P0155 (HO2S HEATER CIRCUIT MALFUNCTION) can cause Code P0153 to set. Repair heater circuit before proceeding with this chart.
- An exhaust leak 6-12" away from HO2S in either direction can cause Code P0153 to set. Thoroughly inspect exhaust system for leaks.
- An HO2S that is contaminated by oil will appear Dark Brown. An HO2S that is contaminated by coolant will be Whitish Green in appearance.
- Certain RTV silicone gasket materials release vapors that can contaminate the HO2S. Silicone in the fuel can cause silica contamination. If sensor appears to be contaminated by silica, and all other sealants are non-silica base, advise customer to select a different fuel company. A missing fuel filler restrictor indicates leaded fuel may have been used.
Chevrolet Corvette ZR-1 1994 - Diagnostic Aids
To verify repair or to determine if condition is intermittent, monitor OBD-II test status for Code P0153.
Chevrolet Corvette ZR-1 1994 - CODE P0154, BANK 2 OXYGEN SENSOR NO. 1 NO ACTIVITY DETECTED
PCM continuously monitors and stores Heated Oxygen Sensor (HO2S) voltage information. PCM evaluates HO2S voltage samples every 100 seconds to determine the amount of time the HO2S voltage was indicating a rich, lean or an inactive condition. PCM will compare the stored HO2S voltage samples taken within each 100 second sample period and determine statistically if a majority of the samples were above or below a predetermined threshold. PCM can also determine if HO2S voltage is indicating an inactive signal. The inactive signal would spend a majority of the time near the HO2S bias voltage. Code P0154 will set when the following conditions are present.
- Engine is operating in closed loop mode.
- TP sensor angle is between 2 and 10 percent.
- Codes 14, 15, 18, 21, 22, 24, 26, 29, 33, 34, 36, 43, 47, 48, 50, 51, 53, 55, P0116, P0117, P0118, P0171, P0172, P0174, P0175, P1114 and P1115 are not set.
- Majority of HO2S voltage samples are between .356-.497 volt.
- All conditions are met for 102 seconds.
- A failed last test code will occur on the first fault.
- A history code will occur on the second drive cycle with a fault.
Code P0154 will be stored in PCM memory, but will not illuminate Malfunction Indicator Light (MIL). A failed last test code will clear when the fault conditions no longer exist. A history code will clear after 40 ignition cycles without a fault, when the battery has been disconnected for 30 seconds, or when the code clearing feature on the Tech 1 is used.
NOTE: Test numbers refer to numbers on diagnostic chart.
- The OBD-II test status for Code P0154 will be displayed on the Tech 1. If the PCM runs the test for Code P0154 and passes, Tech 1 will indicate YES in the RAN column and YES in the PASS column. If PCM fails the test, Tech 1 will indicate YES in RAN column and NO in PASS column. When PCM detects that the test passed then failed, Tech 1 will indicate YES in RAN column and INT (intermittent) in PASS column. If OBD-II test status does not change in the RAN column, ensure all criteria is met that is required to set Code P0154. Engine must be at normal operating temperature before proceeding with this test. This procedure will require a minimum of 3 minutes to run.
- Jumpering circuits to ground should cause HO2S voltage to become less than .2 volt. With circuits shorted to ground, move related HO2S and PCM harnesses while monitoring HO2S voltage on Tech 1. If voltage increases from less than .2 volt to approximately .45 volt, inspect all connections and wiring for intermittent opens.
- Use only a high impedance DVOM for this test.
- Thoroughly inspect all connections and wiring. If connections and wiring are okay, replace bank 2 HO2S No. 1.
Chevrolet Corvette ZR-1 1994 - Diagnostic Aids
An OBD-II test status that indicates INT means the PCM has failed and passed the test during this ignition cycle.
Chevrolet Corvette ZR-1 1994 - CODE P0155, BANK 2 O2 SENSOR NO. 1 HEATER CIRCUIT MALFUNCTION
PCM supplies a bias voltage (approximately .45 volt) on the Heated Oxygen Sensor (HO2S) signal high and low circuits. Battery voltage is supplied to HO2S heater when ignition is turned on. HO2S voltage changes from a bias voltage range to normal operation as HO2S heater reaches operating temperature. HO2S voltage on a cold engine, typically, changes from a bias voltage to a voltage less than .3 volt as HO2S reaches operating temperature. HO2S voltage could possibly increase to greater than .45 volt depending upon the exhaust gas content.
PCM will run heater test only on a cold start (dependent upon coolant and intake air temperatures) and only once per ignition cycle. PCM will monitor HO2S voltage when engine is started. PCM will determine how much time elapsed when HO2S voltage increases above or decreases below the bias range threshold.
Code P0155 will set if the PCM detects too much time elapsed for the HO2S to enter normal operating range. The time required for HO2S to reach operating temperature is based off of engine coolant temperature. If engine coolant temperature is -40?F (-40?C), HO2S should reach operating temperature within 200 seconds. If engine coolant temperature is 154?F (68?C), HO2S should reach operating temperature within 48 seconds. Code P0155 will set when the following conditions are present.
- Engine is started.
- Intake air and engine coolant temperatures are less than 122?F (50?C).
- Intake air and engine coolant temperatures are within 11?F (6?C) of one another at start-up.
- TP sensor angle is less than 16 percent.
- HO2S voltage remains between .3-.7 volt for more than 200 seconds if engine coolant temperature is -40?F (-40?C), or 48 seconds when engine coolant temperature is greater than 154?F (68?C).
Code P0155 will be stored in PCM memory, but will not illuminate Malfunction Indicator Light (MIL). A failed last test code will clear when the fault conditions no longer exist. A history code will clear after 40 ignition cycles without a fault, when the battery has been disconnected for 30 seconds, or when the code clearing feature on the Tech 1 is used.
NOTE: Test numbers refer to numbers on diagnostic chart.
- If Codes P0135 and P0161 are also set, the ignition feed circuit to heated oxygen sensors may be open. Check oxygen sensor fuse located in instrument panel fuse block. HO2S voltage should change from a bias voltage to less than .3 volt or greater than .7 volt within 48 seconds if engine coolant temperature is greater than 154?F (68?C), or within 200 seconds if engine coolant temperature is -40?F (-40?C).
- A contaminated HO2S should be replaced and the condition causing contamination repaired (silicone, lead, engine oil and coolant, etc.).
Chevrolet Corvette ZR-1 1994 - Diagnostic Aids
Engine must be below the start-up coolant temperature for the PCM to run Code P0155 test. To verify repair or to determine if condition is intermittent, monitor OBD-II test status for Code P0155.
Chevrolet Corvette ZR-1 1994 - CODE P0158, BANK 2 O2 SENSOR NO. 2 HIGH SIGNAL VOLTAGE (RICH)
PCM continuously monitors and stores Heated Oxygen Sensor (HO2S) voltage information. PCM evaluates HO2S voltage samples every 100 seconds to determine the amount of time the HO2S voltage was indicating a rich, lean or an inactive condition. PCM will compare the stored HO2S voltage samples taken within each 100 second sample period and determine statistically if a majority of the samples were above or below a predetermined threshold. PCM can also determine if HO2S voltage is indicating an inactive signal. The inactive signal would spend a majority of the time near the HO2S bias voltage.
Code P0158 will set when the following conditions are present.
- Engine is started.
- Intake air and engine coolant temperatures are less than 122?F (50?C).
- Intake air and engine coolant temperatures are within 11?F (6?C) of one another at start-up.
- TP sensor angle is between 2 and 10 percent for 192 seconds.
- Engine is operating in closed loop mode.
- All conditions are met, and the PCM determined that the HO2S voltage levels were indicating a shorted condition (shorted high) greater than .92 volt.
- A failed last test code will occur on the first fault.
- A history code will occur on the second drive cycle with a fault.
Code P0158 will be stored in PCM memory, but will not illuminate Malfunction Indicator Light (MIL). A failed last test code will clear when the fault conditions no longer exist. A history code will clear after 40 ignition cycles without a fault, when the battery has been disconnected for 30 seconds, or when the code clearing feature on the Tech 1 is used.
NOTE: Test numbers refer to numbers on diagnostic chart.
- If Tech 1 displays bank 2 HO2S No. 2 voltage less than .5 volt, signal circuit is okay. HO2S is faulty.
- With HO2S and PCM disconnected, voltage should not be present on signal circuit. If voltage is present, check for short to signal circuit in HO2S heater power circuit.
Chevrolet Corvette ZR-1 1994 - Diagnostic Aids
To verify repair or to determine if condition is intermittent, monitor OBD-II test status for Code P0158.
Chevrolet Corvette ZR-1 1994 - CODE P0160, BANK 2 OXYGEN SENSOR NO. 2 NO ACTIVITY DETECTED
PCM continuously monitors and stores Heated Oxygen Sensor (HO2S) voltage information. PCM evaluates HO2S voltage samples every 100 seconds to determine the amount of time the HO2S voltage was indicating a rich, lean or an inactive condition. PCM will compare the stored HO2S voltage samples taken within each 100 second sample period and determine statistically if a majority of the samples were above or below a predetermined threshold. PCM can also determine if HO2S voltage is indicating an inactive signal. The inactive signal would spend a majority of the time near the HO2S bias voltage. Code P0160 will set when the following conditions are present.
- Engine is operating in closed loop mode.
- TP sensor angle is between 2 and 10 percent.
- Majority of HO2S voltage samples are between .35-.50 volt.
- All conditions are met for 192 seconds.
- A failed last test code will occur on the first fault.
- A history code will occur on the second drive cycle with a fault.
Code P0160 will be stored in PCM memory, but will not illuminate Malfunction Indicator Light (MIL). A failed last test code will clear when the fault conditions no longer exist. A history code will clear after 40 ignition cycles without a fault, when the battery has been disconnected for 30 seconds, or when the code clearing feature on the Tech 1 is used.
NOTE: Test numbers refer to numbers on diagnostic chart.
- A rear HO2S does not fluctuate as much or as rapid as a front HO2S. Using Tech 1, monitor bank 2 HO2S No. 2 while varying the RPM. Rear HO2S voltage should vary greater than .49 volt and less than .35 volt. If voltage does not respond, an open may be present in signal or ground circuit.
- Grounding circuits should cause Bank 2 HO2S No. 2 voltage to decrease (less than .2 volt).
- Use only a high impedance DVOM for this test. This test determines if an open is present in reference or ground circuit.
Chevrolet Corvette ZR-1 1994 - Diagnostic Aids
To verify repair or to determine if condition is intermittent, monitor OBD-II test status for Code P0160.
Fig. 146: Chevrolet Corvette ZR-1 1994 - Component Locations - Code P0160 Flow Chart
Chevrolet Corvette ZR-1 1994 - CODE P0161, BANK 2 O2 SENSOR NO. 2 HEATER CIRCUIT MALFUNCTION
PCM supplies a bias voltage (approximately .45 volt) on the Heated Oxygen Sensor (HO2S) signal high and low circuits. Battery voltage is supplied to HO2S heater when ignition is turned on. HO2S voltage changes from a bias voltage range to normal operation as HO2S heater reaches operating temperature. HO2S voltage on a cold engine, typically, changes from a bias voltage to a voltage less than .3 volt as HO2S reaches operating temperature. HO2S voltage could possibly increase to greater than .45 volt depending upon the exhaust gas content.
PCM will run heater test only on a cold start (dependent upon coolant and intake air temperatures) and only once per ignition cycle. PCM will monitor HO2S voltage when engine is started. PCM will determine how much time elapsed when HO2S voltage increases above or decreases below the bias range threshold.
Code P0161 will set if the PCM detects too much time elapsed for the HO2S to enter normal operating range. The time required for HO2S to reach operating temperature is based off of engine coolant temperature. If engine coolant temperature is -40?F (-40?C), HO2S should reach operating temperature within 240 seconds. If engine coolant temperature is 154?F (68?C), HO2S should reach operating temperature within 100 seconds. Code P0161 will set when the following conditions are present.
- Engine is started.
- Intake air and engine coolant temperatures are less than 122?F (50?C).
- Intake air and engine coolant temperatures are within 11?F (6?C) of one another at start-up.
- TP sensor angle is less than 94 percent.
- HO2S voltage remains between .3-.7 volt for more than 240 seconds if engine coolant temperature is -40?F (-40?C), or 100 seconds when engine coolant temperature is greater than 154?F (68?C).
Code P0161 will be stored in PCM memory, but will not illuminate Malfunction Indicator Light (MIL). A failed last test code will clear when the fault conditions no longer exist. A history code will clear after 40 ignition cycles without a fault, when the battery has been disconnected for 30 seconds, or when the code clearing feature on the Tech 1 is used.
NOTE: Test numbers refer to numbers on diagnostic chart.
- If Codes P0135 and P0155 are also set, the ignition feed circuit to heated oxygen sensors may be open. Check oxygen sensor fuse located in instrument panel fuse block. HO2S voltage should change from a bias voltage to less than .3 volt or greater than .7 volt within 100 seconds if engine coolant temperature is greater than 154?F (68?C), or within 240 seconds if engine coolant temperature is -40?F (-40?C).
- A contaminated HO2S should be replaced and the condition causing contamination repaired (silicone, lead, engine oil and coolant, etc.).
Chevrolet Corvette ZR-1 1994 - Diagnostic Aids
Engine must be below the start-up coolant temperature for the PCM to run Code P0161 test. To verify repair or to determine if condition is intermittent, monitor OBD-II test status for Code P0161.
Fig. 149: Chevrolet Corvette ZR-1 1994 - Component Locations - Code P0161A Flow Chart
Chevrolet Corvette ZR-1 1994 - CODE P0171, BANK 1 FUEL TRIM SYSTEM TOO LEAN
A closed loop air/fuel metering system is used to provide the best possible combination of driveability, fuel economy and emission control. While in closed loop, PCM monitors oxygen sensor signal voltage and adjusts fuel delivery based on signal voltage. The Tech 1 monitors fuel trim values, and will indicate a change made to fuel delivery by the long and short term fuel trim values.
Ideal fuel trim values are approximately 128. If oxygen sensor signal indicates a lean condition, the PCM will add fuel, resulting in a fuel trim value greater than 128. If a rich condition is detected, fuel trim values will be less than 128, indicating that the PCM is reducing the amount of fuel delivered. PCM will set Code P0171 if an excessively lean condition is detected. Code P0171 will set when the following conditions are present.
- Engine fuel system is operating in closed loop.
- Fuel trim is enabled.
- BARO is greater than 10.2 psi (70 kPa).
- TP sensor angle is less than 70 percent.
- Engine RPM is 500-4000 RPM.
- MAP is 2.9-13.1 psi (20-90 kPa).
- IAT is -22?F (-30?C) and 140?F (60?C).
- ECT is 140?F (60?C) and 239?F (115?C).
- MAF is 5 grams per second and 100 grams per second.
- Vehicle speed is less than 75 MPH.
- EVAP canister purge duty cycle is less than 75 percent.
- Codes P0114, P0115, P0116, P0117, P0118, P0133, P0134, P0153 and P0154 are not set.
- All conditions are met for 10 seconds.
- Average short term fuel trim is 138.
- Average long term fuel trim is 155.
Code P0171 will be stored in PCM memory, but will not illuminate Malfunction Indicator Light (MIL). A failed last test code will clear when the fault conditions no longer exist. A history code will clear after 40 ignition cycles without a fault, when the battery has been disconnected for 30 seconds, or when the code clearing feature on the Tech 1 is used.
NOTE: Test numbers refer to numbers on diagnostic chart.
- Codes P0171 and P0174 set at the same time indicates both banks are operating lean. Inspect components/systems that could cause this condition (MAF, vacuum leak, fuel contamination, etc.).
- If bank 1 is operating lean, short term fuel trim will be near 138, and long term fuel trim will be near 155. These parameters are an average of all fuel trim cells.
- If fuel pressure is too low, system will go lean. Codes P0171 and P0174 may set if fuel pressure is too low.
- A lean condition will be caused if the air pump is operating in closed loop.
- MAF sensor could cause a lean condition, but not set a MAF code. If lean condition no longer exists when MAF sensor is disconnected, replace MAF sensor. Visually/physically inspect both sensors for contamination. If contamination is evident, find cause of contamination (lead, silicone, heavy engine oil/coolant consumption, etc.).
Chevrolet Corvette ZR-1 1994 - Diagnostic Aids
To verify repair or to determine if condition is intermittent, monitor OBD-II test status for Code P0171.
Chevrolet Corvette ZR-1 1994 - CODE P0172, BANK 1 FUEL TRIM SYSTEM TOO RICH (1 Of 2)
A closed loop air/fuel metering system is used to provide the best possible combination of driveability, fuel economy and emission control. While in closed loop, PCM monitors oxygen sensor signal voltage and adjusts fuel delivery based on signal voltage. The Tech 1 monitors fuel trim values, and will indicate a change made to fuel delivery by the long and short term fuel trim values.
Ideal fuel trim values are approximately 128. If oxygen sensor signal indicates a lean condition, the PCM will add fuel, resulting in a fuel trim value greater than 128. If a rich condition is detected, fuel trim values will be less than 128, indicating that the PCM is reducing the amount of fuel delivered. PCM will set Code P0172 if an excessively rich condition is detected.
Code P0172 will set when the following conditions are present.
- Engine fuel system is operating in closed loop.
- Fuel trim is enabled.
- BARO is greater than 10.2 psi (70 kPa).
- TP sensor angle is less than 70 percent.
- Engine RPM is 500-4000 RPM.
- MAP is 2.9-13.1 psi (20-90 kPa).
- IAT is -22?F (-30?C) and 140?F (60?C).
- ECT is 140?F (60?C) and 239?F (115?C).
- MAF is 5 grams per second and 100 grams per second.
- Vehicle speed is less than 75 MPH.
- EVAP canister purge duty cycle is less than 75 percent.
- Codes P0114, P0115, P0116, P0117, P0118, P0133, P0134, P0153 and P0154 are not set.
- All conditions are met for 10 seconds.
- Average short term fuel trim is 112.
- Average long term fuel trim is 118.
Code P0172 will be stored in PCM memory, but will not illuminate Malfunction Indicator Light (MIL). A failed last test code will clear when the fault conditions no longer exist. A history code will clear after 40 ignition cycles without a fault, when the battery has been disconnected for 30 seconds, or when the code clearing feature on the Tech 1 is used.
NOTE: Test numbers refer to numbers on diagnostic chart.
- If bank 1 is operating rich, short term fuel trim will be near 112, and long term fuel trim will be near 118. These parameters are an average of all fuel trim cells.
- Codes P0172 and P0174 set at the same time indicates both banks are operating rich. Inspect components/systems that could cause this condition.
- Inspect components/systems that will cause one bank to be rich. Visually/physically inspect all injector driver circuits for short to ground.
Chevrolet Corvette ZR-1 1994 - Diagnostic Aids
To verify repair or to determine if condition is intermittent, monitor OBD-II test status for Code P0172.
Chevrolet Corvette ZR-1 1994 - CODE P0172, BANK 1 FUEL TRIM SYSTEM TOO RICH (2 OF 2)
NOTE: Test numbers refer to numbers on diagnostic chart.
- Ignition may have to be cycled a couple of times to build pressure.
- MAF sensor could cause a rich condition. If rich condition no longer exists, replace MAF sensor.
- If sensors appear to be contaminated, condition causing contamination must be repaired before installing new sensors.
Chevrolet Corvette ZR-1 1994 - CODE P0174, BANK 2 FUEL TRIM SYSTEM TOO LEAN
A closed loop air/fuel metering system is used to provide the best possible combination of driveability, fuel economy and emission control. While in closed loop, PCM monitors oxygen sensor signal voltage and adjusts fuel delivery based on signal voltage. The Tech 1 monitors fuel trim values, and will indicate a change made to fuel delivery by the long and short term fuel trim values.
Ideal fuel trim values are approximately 128. If oxygen sensor signal indicates a lean condition, the PCM will add fuel, resulting in a fuel trim value greater than 128. If a rich condition is detected, fuel trim values will be less than 128, indicating that the PCM is reducing the amount of fuel delivered. PCM will set Code P0174 if an excessively lean condition is detected.
Code P0174 will set when the following conditions are present.
- Engine fuel system is operating in closed loop.
- Fuel trim is enabled.
- BARO is greater than 10.2 psi (70 kPa).
- TP sensor angle is less than 70 percent.
- Engine RPM is 500-4000 RPM.
- MAP is 2.9-13.1 psi (20-90 kPa).
- IAT is -22?F (-30?C) and 140?F (60?C).
- ECT is 140?F (60?C) and 239?F (115?C).
- MAF is 5 grams per second and 100 grams per second.
- Vehicle speed is less than 75 MPH.
- EVAP canister purge duty cycle is less than 75 percent.
- Codes P0114, P0115, P0116, P0117, P0118, P0133, P0134, P0153 and P0154 are not set.
- All conditions are met for 10 seconds.
- Average short term fuel trim is 138.
- Average long term fuel trim is 155.
Code P0174 will be stored in PCM memory, but will not illuminate Malfunction Indicator Light (MIL). A failed last test code will clear when the fault conditions no longer exist. A history code will clear after 40 ignition cycles without a fault, when the battery has been disconnected for 30 seconds, or when the code clearing feature on the Tech 1 is used.
NOTE: Test numbers refer to numbers on diagnostic chart.
- Codes P0171 and P0174 set at the same time indicates both banks are operating lean. Inspect components/systems that could cause this condition (MAF, vacuum leak, fuel contamination, etc.).
- If Bank 2 is operating lean, short term fuel trim will be near 138, and long term fuel trim will be near 155. These parameters are an average of all fuel trim cells.
- If fuel pressure is too low, system will go lean. Codes P0171 and P0174 may set if fuel pressure is too low.
- A lean condition will be caused if the air pump is operating in closed loop.
- MAF sensor could cause a lean condition, but not set a MAF code. If lean condition no longer exists when MAF sensor is disconnected, replace MAF sensor.
Chevrolet Corvette ZR-1 1994 - Diagnostic Aids
Visually/physically inspect both sensors for contamination. If contamination is evident, find cause of contamination (lead, silicone, heavy engine oil/coolant consumption, etc.). To verify repair or to determine if condition is intermittent, monitor OBD-II test status for Code P0174.
Chevrolet Corvette ZR-1 1994 - CODE P0175, BANK 2 FUEL TRIM SYSTEM TOO RICH (1 OF 2)
A closed loop air/fuel metering system is used to provide the best possible combination of driveability, fuel economy and emission control. While in closed loop, PCM monitors oxygen sensor signal voltage and adjusts fuel delivery based on signal voltage. The Tech 1 monitors fuel trim values, and will indicate a change made to fuel delivery by the long and short term fuel trim values.
Ideal fuel trim values are approximately 128. If oxygen sensor signal indicates a lean condition, the PCM will add fuel, resulting in a fuel trim value greater than 128. If a rich condition is detected, fuel trim values will be less than 128, indicating that the PCM is reducing the amount of fuel delivered. PCM will set Code P0175 if an excessively rich condition is detected.
Code P0175 will set when the following conditions are present.
- Engine fuel system is operating in closed loop.
- Fuel trim is enabled.
- BARO is greater than 10.2 psi (70 kPa).
- TP sensor angle is less than 70 percent.
- Engine RPM is 500-4000 RPM.
- MAP is 2.9-13.1 psi (20-90 kPa).
- IAT is -22?F (-30?C) and 140?F (60?C).
- ECT is 140?F (60?C) and 239?F (115?C).
- MAF is 5 grams per second and 100 grams per second.
- Vehicle speed is less than 75 MPH.
- EVAP canister purge duty cycle is less than 75 percent.
- Codes P0114, P0115, P0116, P0117, P0118, P0133, P0134, P0153 and P0154 are not set.
- All conditions are met for 10 seconds.
- Average short term fuel trim is 112.
- Average long term fuel trim is 118.
Code P0175 will be stored in PCM memory, but will not illuminate Malfunction Indicator Light (MIL). A failed last test code will clear when the fault conditions no longer exist. A history code will clear after 40 ignition cycles without a fault, when the battery has been disconnected for 30 seconds, or when the code clearing feature on the Tech 1 is used.
NOTE: Test numbers refer to numbers on diagnostic chart.
- If bank 2 is operating rich, short term fuel trim will be near 112, and long term fuel trim will be near 118. These parameters are an average of all fuel trim cells.
- Codes P0172 and P0175 set at the same time indicates both banks are operating rich. Inspect components/systems that could cause this condition.
- Inspect components/systems that will cause one bank to be rich. Visually/physically inspect all injector driver circuits for short to ground.
Chevrolet Corvette ZR-1 1994 - Diagnostic Aids
To verify repair or to determine if condition is intermittent, monitor OBD-II test status for Code P0175.
Chevrolet Corvette ZR-1 1994 - CODE P0175, BANK 2 FUEL TRIM SYSTEM TOO RICH (2 OF 2)
NOTE: Test numbers refer to numbers on diagnostic chart.
- Ignition may have to be cycled a couple of times to build pressure.
- MAF sensor could cause a rich condition. If rich condition no longer exists, replace MAF sensor.
- If sensors appear to be contaminated, condition causing contamination must be repaired before installing new sensors.
Chevrolet Corvette ZR-1 1994 - CODE P0420, BANK 2 CATALYST SYS LOW O2 STORAGE CAP INDICATED
A three-way catalytic converter is used to maintain reasonably low emissions of hydrocarbons (HC), carbon monoxide (CO) and oxides of nitrogen (NOx). The catalyst within the converter promotes a chemical reaction which oxidizes the HC and CO present in the exhaust gas, thus converting them into harmless water vapor and carbon dioxide. The catalyst also reduces NOx, converting it to nitrogen and free oxygen.
The PCM is capable of monitoring this process using bank 2 HO2S No. 2. Bank 2 HO2S No. 2, which is located in the exhaust stream past the three-way catalytic converter, produces an output signal which indicates the oxygen storage capacity of the catalyst. This in turn indicates the catalyst's ability to convert exhaust emissions effectively.
Bank 2 HO2S No. 2 signal will be far less active than that produced by bank 2 HO2S No. 1 if the catalyst is properly functioning. PCM will set Code P0420 if a problem exists which causes the PCM to detect excessive bank 2 HO2S No. 2 activity outside of an acceptable range for an extended period of time, indicating that the three-way catalytic converter's oxygen storage capacity is below a threshold considered acceptable. Code P0420 will set when the following conditions are present.
- Engine coolant temperature is greater than 185?F (85?C).
- Mass airflow is 14-32 grams per second for 37 seconds.
- Vehicle speed is 25-68 MPH.
- Codes 14, 15, 18, 24, 26, 43, 48, 50, 51, 53, 55, 63, 64, 65, 72, P0116, P0117, P0118, P0151, P0152, P0153, P0154, P0155, P0158, P0160, P0175, P1114, P1115, P1153 and P1158 are not set.
- Above conditions are met for at least 2 minutes.
- PCM determines bank 2 HO2S No. 2 activity to be excessive.
Code P0420 will be stored in PCM memory, but will not illuminate Malfunction Indicator Light (MIL). A failed last test code will clear when the fault conditions no longer exist. A history code will clear after 40 ignition cycles without a fault, when the battery has been disconnected for 30 seconds, or when cleared using the Tech 1.
NOTE: Test numbers refer to numbers on diagnostic chart.
- This chart checks for conditions that can cause the three-way catalytic converter efficiency to appear degraded. Inspect and repair exhaust system as necessary. Also inspect bank 2 HO2S No. 2 pigtail and engine harness for any damage that may cause an intermittent fault in high or low oxygen sensor circuit.
- If three-way catalytic converter replacement is necessary, ensure another condition is not present that may have caused the catalyst to become damaged (misfire, high engine oil consumption or coolant consumption, retarded spark timing or weak spark). Correct engine misfire or mechanical fault before replacing the three-way catalytic converter to avoid damaging the replacement converter.
Chevrolet Corvette ZR-1 1994 - Diagnostic Aids
In areas in which the conditions cannot be easily maintained, especially in urban areas, it may be difficult to run the catalyst monitor test. Use the following procedure to minimize the amount of driving required to complete test.
- Allow engine to warm completely.
- Place vehicle in Park. Using Tech 1, monitor mass airflow. Hold part throttle to maintain a reading of greater than 14 grams per second for at least 2 minutes. This will achieve the warm catalyst criteria for running test.
- Operate the vehicle within the above conditions required to cause Code P0420 to set. If stopping is required, maintain the warm catalyst criteria by placing vehicle in Park or Neutral and holding part throttle to maintain a mass airflow reading of greater than 14 grams per second for the duration of the stop.
Chevrolet Corvette ZR-1 1994 - CODE P1114, ENGINE COOLANT TEMP INTERMITTENT LOW INPUT VOLTAGE
ECT sensor uses a thermistor to control signal voltage to PCM. PCM applies and monitors approximately 5 volts on circuit to ECT sensor. When engine coolant is cold, sensor (thermistor) resistance is high and PCM will sense a high signal voltage. As engine coolant warms up, sensor resistance becomes less and PCM voltage drops. Code P1114 will set when the following conditions are present.
- PCM indicates ECT sensor signal voltage is low (less than 1 volt) for 2 seconds.
- A failed last test code will occur on the first fault.
- A history code will occur on the second drive cycle with a fault.
Code P1114 will be stored in PCM memory, but will not illuminate Malfunction Indicator Light (MIL). A failed last test code will clear when the fault conditions no longer exist. A history code will clear after 40 ignition cycles without a fault, when the battery has been disconnected for 30 seconds, or when cleared using Tech 1.
NOTE: Test numbers refer to numbers on diagnostic chart.
- A hard failure is indicated if Tech 1 displays a temperature greater than 284?F (140?C). Code P0117 chart should be used. If a normal temperature is indicated, inspect circuit for a short to ground from ECT sensor, back to PCM.
- Sensor wire is intermittently shorted to ground when the ECT harness is removed, and the Tech 1 changes from a normal temperature to greater than 284?F (140?C). Thoroughly inspect ECT harness for a bare wire that is contacting ground.
Chevrolet Corvette ZR-1 1994 - Diagnostic Aids
Viewing freeze frame data with the Tech 1, or using the Tech 1's snapshot feature may assist in locating an intermittent failure. To verify repair or to determine if condition is intermittent, monitor OBD-II test status for Code P1114.
Chevrolet Corvette ZR-1 1994 - CODE P1115, ENGINE COOLANT TEMP INTERMITTENT HIGH INPUT VOLTAGE
ECT sensor uses a thermistor to control signal voltage to PCM. PCM applies and monitors about 5 volts to coolant sensor. When engine coolant is cold, sensor (thermistor) resistance is high and PCM will sense a high signal voltage. As engine coolant warms up, sensor resistance becomes less and PCM voltage drops. Code P1115 will set when the following conditions are present.
- PCM indicates ECT sensor signal voltage is high (greater than 4.8 volts) for 30 seconds.
Code P1115 will be stored in PCM memory, but will not illuminate Malfunction Indicator Light (MIL). A failed last test code will clear when the fault conditions no longer exist. A history code will clear after 40 ignition cycles without a fault, when the battery has been disconnected for 30 seconds, or when cleared using Tech 1.
NOTE: Test numbers refer to numbers on diagnostic chart.
- A hard failure is indicated if Tech 1 shows a temperature of -40?F (-40?C) or less. Code P0118 chart should be used. If a normal temperature is indicated, inspect circuits for an intermittent open from ECT sensor, back to PCM.
- Sensor circuits are intermittently opening when the ECT harness is removed, and the Tech 1 changes from a normal temperature to -40?F (-40?C). Thoroughly inspect harness and ECT/PCM connectors for intermittently opening.
- DO NOT replace ECT sensor unless circuits have been thoroughly inspected from ECT to PCM.
Chevrolet Corvette ZR-1 1994 - Diagnostic Aids
Viewing freeze frame data with the Tech 1, or using the Tech 1's snapshot feature may assist in locating an intermittent failure. To verify repair or to determine if condition is intermittent, monitor OBD-II test status for Code P1115.
Chevrolet Corvette ZR-1 1994 - CODE P1133, BANK 1 OXYGEN SENSOR NO. 1 NOT ENOUGH SWITCHES
PCM monitors Heated Oxygen Sensor (HO2S) activity for 100 seconds. During this monitoring period, PCM counts the number of times that the HO2S switches from rich to lean and from lean to rich. Code P1133 will set if PCM determines that HO2S voltage did not switch enough times. Code P1133 will set when the following conditions are present.
- Engine is started.
- Intake air and engine coolant temperatures are less than 122?F (50?C).
- Intake air and engine coolant temperatures are within 11?F (6?C) of one another at start-up.
- TP sensor angle is between 2 and 10 percent for 100 seconds.
- Engine is operating in closed loop mode.
- Codes 14, 15, 18, 21, 22, 24, 26, 29, 33, 34, 36, 43, 47, 48, 50, 51, 53, 55, P0116, P0117, P0118, P0171, P0172, P0174, P0175, P1114 and P1115 are not set.
- All above conditions are met, and the number of lean to rich and rich to lean switches are less than 48.
A lean to rich switch is determined when the HO2S voltage changes from less than .3 volt to greater than .6 volt. A rich to lean switch is determined when the HO2S voltage changes from greater than .6 volt to less than .3 volt.
Code P1133 will be stored in PCM memory, but will not illuminate Malfunction Indicator Light (MIL). A failed last test code will clear when the fault conditions no longer exist. A history code will clear after 40 ignition cycles without a fault, when the battery has been disconnected for 30 seconds, or when cleared using Tech 1.
NOTE: Test numbers refer to numbers on diagnostic chart.
- Code P0135 (HO2S HEATER CIRCUIT MALFUNCTION) will cause Code P1133 to set. Repair Code P0135 before proceeding with this chart. Codes P1133 and P1153 set at the same time indicates a malfunction that will affect both banks. Inspect components/systems that will cause HO2S voltages to hang low (lean) or high (rich).
- Inspect components/systems that will only affect one bank (exhaust leaks, faulty HO2S, ignition fault, injector fault, etc.).
- Certain RTV silicone gasket materials release vapors that can contaminate the HO2S. Silicone in the fuel can cause contamination (Gray colored deposits). If sensor appears to be contaminated by silicone, and all other sealants are non-silicone base, advise customer to select a different fuel company. High engine oil consumption or coolant consumption may cause a sensor to be sluggish. Also check for lead contamination. A missing fuel filler restrictor indicates leaded fuel may have been used.
- If contamination is found, repair condition that caused contamination before replacing heated oxygen sensors.
Chevrolet Corvette ZR-1 1994 - Diagnostic Aids
If components/systems are okay, check for an intermittent open in HO2S heater circuits. A HO2S heater that is inoperative will cause Code P1133 to set. To verify repair or to determine if condition is intermittent, monitor OBD-II test status for Code P1133.
Chevrolet Corvette ZR-1 1994 - CODE P1153, BANK 2 OXYGEN SENSOR NO. 1 NOT ENOUGH SWITCHES
PCM monitors Heated Oxygen Sensor (HO2S) activity for 100 seconds. During this monitoring period, PCM counts the number of times that the HO2S switches from rich to lean and from lean to rich (cross counts). Code P1153 will set if PCM determines that HO2S voltage did not switch enough times.
Code P1153 will set when the following conditions are present.
- Engine is started.
- Intake air and engine coolant temperatures are less than 122?F (50?C).
- Intake air and engine coolant temperatures are within 11?F (6?C) of one another at start-up.
- TP sensor angle is between 2 and 10 percent for 100 seconds.
- Engine is operating in closed loop mode.
- Codes 14, 15, 18, 21, 22, 24, 26, 29, 33, 34, 36, 43, 47, 48, 50, 51, 53, 55, P0116, P0117, P0118, P0171, P0172, P0174, P0175, P1114 and P1115 are not set.
- All above conditions are met, and the number of lean to rich and rich to lean switches are less than 48.
A lean to rich switch is determined when the HO2S voltage changes from less than .3 volt to greater than .6 volt. A rich to lean switch is determined when the HO2S voltage changes from greater than .6 volt to less than .3 volt.
Code P1153 will be stored in PCM memory, but will not illuminate Malfunction Indicator Light (MIL). A failed last test code will clear when the fault conditions no longer exist. A history code will clear after 40 ignition cycles without a fault, when the battery has been disconnected for 30 seconds, or when cleared using Tech 1.
NOTE: Test numbers refer to numbers on diagnostic chart.
- Code P0155 will cause Code P1153 to set. Repair Code P0155 before proceeding with this chart. Codes P1133 and P1153 that are set at the same time indicate a malfunction that will affect both banks. Inspect components/systems that will cause HO2S voltages to hang low (lean) or high (rich).
- Inspect components/systems that will only affect one bank (exhaust leaks, faulty HO2S, ignition fault, injector fault, etc.).
- Certain RTV silicone gasket materials release vapors that can contaminate the HO2S. Silicone in the fuel can cause silica contamination. If sensor appears to be contaminated by silicone (Gray colored deposits), and all other sealants are non-silicone base, advise customer to select a different fuel company. High engine oil consumption or coolant consumption may cause a sensor to be sluggish. Also check for lead contamination. A missing fuel filler restrictor indicates leaded fuel may have been used.
- If contamination is found, repair condition that caused contamination before replacing heated oxygen sensors.
Chevrolet Corvette ZR-1 1994 - Diagnostic Aids
If components/systems are okay, check for an intermittent open in HO2S heater circuits. A HO2S heater that is inoperative will cause Code P1153 to set. To verify repair or to determine if condition is intermittent, monitor OBD-II test status for Code P1153.
Chevrolet Corvette ZR-1 1994 - CODE P1158, BANK 2 OXYGEN SENSOR NO. 2 SHIFTED RICH
PCM continuously monitors and stores Heated Oxygen Sensor (HO2S) voltage information. PCM evaluates HO2S voltage samples every 100 seconds to determine the amount of time the HO2S voltage was indicating a rich, lean or an inactive condition. PCM will compare the stored HO2S voltage samples taken within each 100 second sample period and determine statistically if a majority of the samples were above or below a predetermined threshold. PCM can also determine if HO2S voltage is indicating an inactive signal. The inactive signal would spend a majority of the time near the HO2S bias voltage. Code P1158 will set when the following conditions are present.
- Engine is operating in closed loop mode.
- TP sensor angle is between 2 and 10 percent.
- Majority of HO2S voltage samples are .709-.923 volt.
- All conditions are met for 192 seconds.
- A failed last test code will occur on the first fault.
- A history code will occur on the second drive cycle with a fault.
Code P1158 will be stored in PCM memory, but will not illuminate Malfunction Indicator Light (MIL). A failed last test code will clear when the fault conditions no longer exist. A history code will clear after 40 ignition cycles without a fault, when the battery has been disconnected for 30 seconds, or when cleared using Tech 1.
NOTE: Test numbers refer to numbers on diagnostic chart.
- Engine operating rich on the right bank will have an effect on the rear HO2S. If Codes P0152/P0174 are set, refer to appropriate chart. An engine misfire can also cause Code P1158 to set. Correct engine misfire before proceeding with this chart.
- Circuits jumpered to ground should cause HO2S voltage to go low, and will determine if HO2S wiring and PCM are okay.
- An HO2S heater battery feed circuit shorted to the HO2S signal wire can cause Code P1158 to set.
Chevrolet Corvette ZR-1 1994 - Diagnostic Aids
Thoroughly inspect components/systems that will cause the right side of the engine (bank 2) to operate rich. The rear HO2S has no fuel control responsibilities. It is used only for catalyst monitoring. To verify repair or to determine if condition is intermittent, monitor OBD-II test status for Code P1158.
Chevrolet Corvette ZR-1 1994 - 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.