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Chevrolet Corvette ZR-1 1993 - G - TESTS W/CODES - 5.7L 1993 ENGINE PERFORMANCE General Motors Self-Diagnostics - 5.7L "Y" Body ECM/PCM
Chevrolet Corvette ZR-1 1993 - INTRODUCTION
Most engine control problems are the result of mechanical breakdowns, poor electrical connections or damaged vacuum hoses. Before considering the computer system as a possible cause of problems, perform checks and inspections covered in BASIC TESTING article in this section. Failure to do so may result in lost diagnostic time.
If no faults were found while performing BASIC TESTING , proceed with DIAGNOSTIC PROCEDURE under SELF-DIAGNOSTIC SYSTEM . If no fault codes or only a non-running Code 12 is present and driveability problems exist, proceed to TESTS W/O CODES article in this section for diagnosis by symptom (i.e., ROUGH IDLE, NO START, etc.). If only intermittent codes are present, see INTERMITTENTS in TESTS W/O CODES article in this section.
Chevrolet Corvette ZR-1 1993 - SELF-DIAGNOSTIC SYSTEM
NOTE: Electronic Control Module (ECM) may also be referred to as Powertrain Control Module (PCM) in some diagnostic charts and figures. Terms are used interchangeably.
Control module is equipped with a self-diagnostic system, which detects system failures or abnormalities. When a malfunction occurs, control module will illuminate SERVICE ENGINE SOON light located on instrument panel. SERVICE ENGINE SOON light may also be referred to as the Malfunction Indicator Light (MIL). When malfunction is detected and light is turned on, a corresponding trouble code will be stored in control module memory. To retrieve stored codes, see RETRIEVING CODES (NON-SCAN) . Malfunctions are recorded as hard failures or as intermittent failures.
Chevrolet Corvette ZR-1 1993 - HARD FAILURES
Hard failures cause SERVICE ENGINE SOON light to glow and remain on until malfunction is repaired. If light comes on and remains on (light may flash) during vehicle operation, cause of malfunction must be determined using diagnostic (code) charts. If a sensor fails, control module will use a substitute value in its calculations to continue engine operation. In this condition, vehicle is functional, but it will most likely encounter degraded driveability.
Chevrolet Corvette ZR-1 1993 - INTERMITTENT FAILURES
Intermittent failures cause SERVICE ENGINE SOON light to flicker or glow and go out about 10 seconds after intermittent fault goes away. Corresponding trouble code, however, will be retained in control module memory. If related fault does not reoccur within 50 engine starts, related trouble code will be erased from control module memory. Intermittent failures may be caused by sensor, connector or wiring related problems. See INTERMITTENTS in TESTS W/O CODES article in this section.
Chevrolet Corvette ZR-1 1993 - DIAGNOSTIC PROCEDURE
Diagnosis of computerized engine control system should be performed in following order:
- Ensure all engine systems not related to computer system are operating properly. DO NOT proceed with testing unless all other problems have been repaired. DIAGNOSTIC CIRCUIT CHECK must be performed before using trouble code charts. See BASIC TESTING article in this section.
- If trouble codes were displayed (other than Code 12), determine whether codes are hard or intermittent trouble codes. Hard codes will cause SERVICE ENGINE SOON light to glow continuously while engine is running. See HARD OR INTERMITTENT TROUBLE CODE DETERMINATION . For diagnosing hard codes, proceed to appropriate trouble code chart. For diagnosing intermittent codes, proceed to INTERMITTENTS in BASIC TESTING article in this section. Exceptions are Code 13, 15, 24, 44 and 45 charts, which may be used to help diagnose intermittent codes.
- If no trouble codes were displayed and a driveability problem exists, refer to SYMPTOMS in TESTS W/O CODES article in this section. Doing so will identify proper system or component to check in I - SYS/COMP TESTS article in this section.
- After necessary repairs are made, clear trouble codes and perform FIELD SERVICE MODE CHECK in BASIC TESTING article in this section.
NOTE: For information on retrieving codes using a scan tester, refer to user and reference manuals supplied with tester.
Chevrolet Corvette ZR-1 1993 - RETRIEVING CODES (NON-SCAN)
NOTE: Inserting jumper wire into test and ground terminals of ALDL connector with engine running will cause fuel injected vehicles to enter field service mode. Flashes of SERVICE ENGINE SOON light will not indicate codes if this is done. See FIELD SERVICE MODE CHECK in BASIC TESTING article in this section.
- Turn ignition on. DO NOT start engine. SERVICE ENGINE SOON light should glow. Locate Assembly Line Data Link (ALDL) connector attached to control module wiring harness. Most ALDL connectors are located under dash on driver side of vehicle. For exact location of ALDL, see COMPONENT LOCATIONS in I - SYS/COMP TESTS article in this section. Insert jumper wire from terminal "B" (diagnostic test terminal) to terminal "A" (ground) of ALDL connector. See Fig. 1 .
- SERVICE ENGINE SOON light should begin to flash codes. Each code will be repeated 3 times. If codes are not flashed or SERVICE ENGINE SOON light does not glow, perform DIAGNOSTIC CIRCUIT CHECK in BASIC TESTING article in this section. To exit diagnostic mode, turn ignition off and remove jumper wire from ALDL connector.
Fig. 1: Chevrolet Corvette ZR-1 1993 - Component Locations - ALDL Connector Terminal ID
Chevrolet Corvette ZR-1 1993 - READING TROUBLE CODES
Control module stores component failure information under a related trouble code which can be recalled for diagnosis and repair. Trouble codes may be read by counting flashes of SERVICE ENGINE SOON light or by reading digital display on a scan tester. Scan tester is faster to use, more accurate and capable of reading information which otherwise would necessitate testing individual control module and sensor/solenoid connector terminals using a digital voltmeter. See SCAN TESTER USAGE and SCAN DATA .
NOTE: When using most scan testers, a time delay exists between serial data updates. For instantaneous response, a digital voltmeter must be used.
If scan tester is not available, reading flashes of SERVICE ENGINE SOON light is possible by grounding diagnostic test terminal "B" of ALDL with ignition on and engine off. See Fig. 1 . For example, "FLASH, FLASH, pause, FLASH, longer pause" identifies Code 21. First series of flashes is first digit of trouble code. Second series of flashes is second digit of trouble code. Trouble codes are displayed starting with lowest numbered code. Each code is displayed 3 times. Codes will continue to repeat as long as ALDL test terminal is grounded.
NOTE: Trouble codes will be recorded at various operating times. Some codes require operation of that sensor or switch for 5 seconds; others require operation for 5 minutes or longer at normal operating temperature, vehicle speed and load. Therefore, some codes may not set in a service bay operational mode and may require road testing vehicle in order to duplicate condition under which code will set.
Chevrolet Corvette ZR-1 1993 - TROUBLE CODE DEFINITION
Chevrolet Corvette ZR-1 1993 ECM/PCM TROUBLE CODE DEFINITION
Code No. Circuit Affected 12 (1) No RPM Reference Pulse 13 Oxygen Sensor Circuit Open Left Oxygen Sensor Circuit Open (Dual-Sensor Models) 14 Coolant Temperature Sensor Signal Voltage Low 15 Coolant Temperature Sensor Signal Voltage High 16 Low Resolution Pulse (5.7L VIN P) 21 TPS Signal Voltage High 22 TPS Signal Voltage Low 23 MAT Sensor Signal Voltage High 24 Vehicle Speed Sensor 25 MAT Sensor Signal Voltage Low 26 Quad-Driver Error (5.7L) 27 Or 28 Quad-Driver Error (5.7L VIN P) 32 EGR System Error 33 MAP Sensor Signal Voltage High 34 MAP Sensor Signal Voltage Low 35 IAC Idle Speed Error 36 High Resolution Pulse (5.7L VIN P) 41 Opti-Spark EST Circuit 42 Opti-Spark EST Circuit Grounded 43 ESC Error 44 Lean Exhaust Indication Left Lean Exhaust Indication (Dual-Sensor Models) 45 Rich Exhaust Indication Left Rich Exhaust Indication (Dual-Sensor Models) 51 Faulty PROM, MEM-CAL Or ECM/PCM 52 Faulty/Missing CAL-PAC Or MEM-CAL Low Engine Oil Temperature (5.7L "Y" Body) 53 System Overvoltage 54 Fuel Pump Voltage Low 55 Fuel Lean Monitor 61 A/C System Performance 62 High Engine Oil Temperature 63 Right Oxygen Sensor Circuit Open (Dual-Sensor Models) 64 Right Oxygen Sensor Lean (Dual-Sensor Models) 65 Right Oxygen Sensor Rich (Dual-Sensor Models) 66 A/C Pressure Sensor 67 A/C Pressure Sensor 68 A/C Relay Circuit Shorted 69 A/C Compressor Relay 72 Gear Switch Circuit 85 PROM Error 87 EEPROM Error
(1) Display of a Code 12 is normal when reference pulses are not being received by control module (engine not running).
NOTE: Use trouble code charts only if SERVICE ENGINE SOON light is illuminated (indicating a current problem exists). Exceptions are Code 13, 15, 24, 44 and 45 charts, which may be used to help diagnose intermittent codes. Anytime control module-related Codes 51, 52 or 55 are displayed with another code, start with 50-series code, and then proceed to lower numbered codes.
Chevrolet Corvette ZR-1 1993 - HARD OR INTERMITTENT TROUBLE CODE DETERMINATION
During any diagnostic procedure, determine if codes are hard failure codes or intermittent failure codes. Diagnostic charts will not usually help analyze intermittent codes. To determine hard codes and intermittent codes:
- Manually enter diagnostic mode. Read and record all stored trouble codes. Exit diagnostic mode, and clear trouble codes. See CLEARING TROUBLE CODES .
- Apply parking brake, and place transmission in Neutral or Park. Block drive wheels, and start engine. SERVICE ENGINE SOON light should go out. Run warm engine at specified curb idle for 2 minutes and note SERVICE ENGINE SOON light.
- If SERVICE ENGINE SOON light comes on, manually enter diagnostic mode. Read and record trouble codes. This will reveal hard failure codes. Codes 13, 15, 24, 44 and 45 may require a road test to reset hard failure after trouble codes were cleared.
- If SERVICE ENGINE SOON light does not come on, all stored trouble codes were intermittent failures, except as noted above.
Chevrolet Corvette ZR-1 1993 - CLEARING TROUBLE CODES
Turn ignition switch to ON position, and ground diagnostic test terminal "B" at ALDL connector. See Fig. 1 . Turn ignition switch to OFF position, and remove control module fuse from fuse block for 10 seconds. Replace fuse. Remove diagnostic terminal ground lead. If fuse cannot be located, pigtail at battery can be disconnected. When power to ECM is removed, degraded driveability may be exhibited until control module "relearns" optimum operational parameters.
Chevrolet Corvette ZR-1 1993 - ECM/PCM LOCATION
On most models, engine control module is located behind right or left side of dash or behind right or left kick panel. On Corvette, control module is located in left rear corner of engine compartment, next to battery. See COMPONENT LOCATIONS in I - SYS/COMP TESTS article in this section.
Chevrolet Corvette ZR-1 1993 - DIAGNOSTIC MATERIALS Diagnostic Aids
Diagnostic aids (located in many trouble code charts) are additional tips used to help diagnose trouble codes when inspected circuit is okay. Diagnostic aids may help lead to a definitive solution to trouble code problem.
Chevrolet Corvette ZR-1 1993 - Field Service Mode Check
If ALDL test terminal "B" is grounded with engine running, SERVICE ENGINE SOON light will indicate operational mode of engine. This test confirms proper operation of fuel system and verifies "closed loop" operation. Clear codes and perform this test after any repair is completed. Field service mode check can be found by proceeding to FIELD SERVICE MODE CHECK in BASIC TESTING article in this section.
Chevrolet Corvette ZR-1 1993 - SPECIAL TOOLS (DIAGNOSTIC)
NOTE: A scan tester plugged into ALDL may be used to read trouble codes and check voltages in system on serial data line (terminal "E", or terminal "M" on P-4 systems). This can save a great deal of time. For additional information, see SCAN TESTER USAGE and SCAN DATA .
Computerized engine control system is most easily diagnosed using scan tester; however, other tools may aid in diagnosing problems if a scan tester is unavailable. These tools are a tachometer, test light, ohmmeter, digital voltmeter with 10-megohm input impedance (minimum), vacuum pump, vacuum gauge, fuel injector test lights (for both TBI and PFI) 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 1993 - SCAN TESTER USAGE
NOTE: Before connecting scan tester to vehicle, diagnostic system should be checked to determine if system is operating properly and if information received will be accurate. This is done by performing DIAGNOSTIC CIRCUIT CHECK located in BASIC TESTING article in this section. If vehicle does not pass diagnostic circuit check, information received may be invalid.
Scan tester is a specialized tester which, when plugged into ALDL, can be used to diagnose on-board computer control systems by providing instant access to circuit voltage information without need to crawl under dash or hood to backprobe sensors and connectors.
Scan tester cuts down diagnostic time dramatically by furnishing input data (voltage signals) which can be compared to specification parameters. See SCAN DATA. They may also furnish information on output device (solenoids and motors) status. However, status parameters only indicate output signals have been sent to devices by control module; they do not indicate whether devices have responded properly to signal. Verify proper response at output device using a voltmeter or test light.
NOTE: Code 12 should always exist when ALDL is grounded with key on and engine not running, but it may not be indicated by all makes of scan testers.
A problem may exist even if trouble codes are not present. About 80 percent of driveability problems occur without trouble codes. Sensors that are out of specification will not set a trouble code but will cause driveability problems.
Using scan tester is easiest method of checking sensor specifications and other data parameters. Tester is also useful in finding intermittent wiring problems by wiggling wiring harnesses and connections (key on, engine off) while observing data parameters. See SCAN DATA .
NOTE: If erroneous voltage signals are suspected, verify tester information using a digital voltmeter and wiring schematic. If non-existent codes are displayed, turn ignition off, remove tester, turn ignition on and ground ALDL test terminal "B". Same codes flashed by SERVICE ENGINE SOON light should be indicated by scan tester.
Chevrolet Corvette ZR-1 1993 - SCAN DATA
NOTE: Information contained in following tables is typical of readings taken on vehicle with engine idling, upper radiator hose hot, closed throttle, transmission in Park or Neutral, "closed loop" status achieved and all accessories off (except as noted in tables). Data parameters are updated every 1 1/4 seconds. On systems using P-4 computers, parameter updates are more frequent. Not all devices and systems are used on all models; following lists only represent most commonly used parameters. For additional information, refer to owner manual furnished with tester.
Chevrolet Corvette ZR-1 1993 SCAN DATA - THROTTLE BODY INJECTION
Tester Position Units Measured Nominal Value A/C Clutch On/Off Off (On With A/C) A/C Request Yes/No No/Yes (With Request) AIR Divert Sol On/Off On (Air To Switching Sol.); Off (Air To Atmosphere) AIR Switching Sol. On/Off On (To Exhaust Manifold); Off (To Catalytic Converter) BARO Volts 3.0 - 4.5 Battery Voltage Volts 13.5 - 14.5 Block Learn Counts 118 - 138 (128 Normal) Brake Switch On/Off On When Engaged Canister Purge Sol On/Off On/Engine Cold (Idle Some) Clear Flood On/Off See Scan Tester Manual Coolant Fan On/Off Off Below 216?F (102?C) Coolant Temp. ?C 85 - 105? (Norm. Temperature) Crank RPM RPM 100 - 900 Cross Counts Counts 0 - 255 Cruise Cont. Sw. On/Off On When Engaged EGR Solenoid On/Off On When Energized EGR Duty Cycle 0 - 100% 0/Closed; 100/Fully Open Fan Relay On/Off On When Energized Fan Request On/Off On With Request Fuel Back-Up Yes/No Yes When Engaged IAC Counts 0 - 50 Ignition/Crank On/Off On With Ignition/Crank Injector Pulse Width Mil./Sec .8 - 3.0 INT (Integrator) Counts 110-145 (128 Normal) Knock Retard (ESC) Counts 0 - 255 Knock Signal Yes/No Yes When Knock Exists MAT ?C 10 - 90? MAP Volts 1.0 (Idle) to 4.5 (WOT) "Open/Closed Loop Status" Ol/Cl Closed/Open During Extended Idle O2 Sensor Millivolts 100 (Lean) To 999 (Rich) P/N Switch P/N/RDL Park/Neutral P/S Switch Norm/Hi Normal PROM I.D. PROM No. Original Factory Number RPM RPM Spec. +/-25 RPM Drive (A/T); Spec. +/-50 RPM Neut. (M/T) Spark Advance Degrees Varies TCC On/Off Off (On With Command) Throttle Angle 0-100% 0 (Idle) To 110 (WOT) TPS Volts 1.25 (Idle) To 5.00 (WOT) Trouble Codes Code No. No Codes Upshift Light (M/T) On/Off Off VSS Or MPH MPH 0 - Actual 3rd Gear Switch On/Off On/3rd & 4th Gear 4th Gear Switch On/Off On/4th Gear
Chevrolet Corvette ZR-1 1993 SCAN DATA - PORT FUEL INJECTION
Tester Position Units Measured Nominal Value A/C Clutch On/Off Off (On With A/C) A/C Request Yes/No No/Yes (With Request) AIR Divert Sol On/Off On (Air To Switching Sol.); Off (Air To Atmosphere) AIR Switching Sol. On/Off On (To Exhaust Manifold); Off (To Catalytic Converter) BARO Volts 3.0 - 4.5 Battery Voltage Volts 13.5 - 14.5 Block Learn Counts 118 - 138 (128 Normal) Canister Purge Sol On/Off On/Engine Cold (Idle Some) Clear Flood On/Off See Scan Tester Manual Coolant Fan On/Off Off Below 216?F (102?C) Coolant Temp. ?C 85 - 105? (Norm. Temperature) Crank RPM RPM 100 - 900 Cross Counts Counts 0 - 255 EGR Solenoid On/Off On When Energized EGR Duty Cycle 0 - 100% 0/Closed; 100/Fully Open Fan Relay On/Off On When Energized Fan Request On/Off On With Request Fuel Back-Up Yes/No Yes When Engaged IAC Counts 0 - 50 Ignition/Crank On/Off On With Ignition/Crank Injector Pulse Width Mil./Sec .8 - 3.0 INT (Integrator) Counts 110-145 (128 Normal) Knock Retard (ESC) Counts 0 - 255 Knock Signal Yes/No Yes When Knock Exists MAT ?C 10 - 90? MAP Volts 1.0 (Idle) to 4.5 (WOT) "Open/Closed Loop Status" Ol/Cl Closed/Open During Extended Idle O2 Sensor Millivolts 100 (Lean) To 999 (Rich) P/N Switch P/N/RDL Park/Neutral P/S Switch Norm/Hi Normal PROM I.D. PROM No. Original Factory Number RPM RPM Spec. +/-25 RPM Drive (A/T); Spec. +/-50 RPM Neut. (M/T) Spark Advance Degrees Varies TCC On/Off Off (On With Command) TPS Volts 1.25 (Idle) To 5.00 (WOT) Throttle Angle 0-100% 0 (Idle) To 110 (WOT) Trouble Codes Code No. No Codes Upshift Light (M/T) On/Off Off VSS Or MPH MPH 0 - Actual Water Injection On/Off On When Injecting 1st Gear Switch On/Off On/1st Gear Only 3rd Gear Switch On/Off On/3rd & 4th Gear 4th Gear Switch On/Off On/4th Gear
Chevrolet Corvette ZR-1 1993 - ECM/PCM CODE CHARTS
NOTE: In following diagnostic tests, schematics and illustrations are courtesy of General Motors Corp.
Chevrolet Corvette ZR-1 1993 - CODE 13 - OPEN OXYGEN SENSOR CIRCUIT
NOTE: The 5.7L (VIN P) engine is equipped with 2 oxygen sensors. On these models, Code 13 will set if the left sensor circuit is open. Code 63 will set if the right sensor circuit is open. Use this chart for Code 63 also and perform tests for applicable sensor.
NOTE: Test numbers refer to numbers on diagnostic chart.
- This tests if problem still exists. Vehicle cannot enter "closed loop" mode if oxygen sensor circuit is open. Code 13 indicates an open in O2 sensor circuit. Code will set if Engine is at normal operating temperature, neither Code 21 nor Code 22 is stored, oxygen sensor voltage is constant within a specified range (.34-.55 volt), throttle angle is greater than idle, a precalibrated amount of time has elapsed since start-up and all conditions have existed for a precalibrated amount of time.
- Determines if oxygen sensor, wiring or control module is at fault. If wiring is good, grounding oxygen sensor wire will cause .45 volt reference supplied by control module to pull low.
- This tests oxygen sensor circuit wiring. Use only a high impedance (10-megohm minimum) digital voltmeter.
Chevrolet Corvette ZR-1 1993 - Diagnostic Aids
Control module will not go into closed loop if Code 13 is set. Code 13 may set if vehicle runs out of fuel or stalls while vehicle is in motion. If oxygen sensor ground becomes loose, a false oxygen sensor reading will occur. This can result in a Code 13 being set. On models equipped with an oxygen sensor heating element, element resistance should be 3.5-14 ohms.
Chevrolet Corvette ZR-1 1993 CODE 13 ECM TERMINAL & CIRCUIT WIRING IDENTIFICATION
Application ECM Terminal Wire Color 5.7L "Y" Body Left O2 Signal D6 Purple Left O2 Ground D17 Tan Right O2 Signal D22 Purple Right O2 Ground D17 Tan
Chevrolet Corvette ZR-1 1993 - CODE 14 - COOLANT TEMPERATURE SENSOR (SIGNAL VOLTAGE LOW)
NOTE: This chart assumes engine cooling system is functioning properly (not overheating). Test numbers refer to numbers on diagnostic chart.
- Code 14 indicates control module has seen low coolant sensor voltage signal (high temperature) at control module terminal for a precalibrated period of time. This checks if conditions for Code 14 still exist.
- This tests for grounded sensor signal line between control module and coolant sensor.
Chevrolet Corvette ZR-1 1993 - Diagnostic Aids
After engine is started, temperature should rise steadily to about 190?F (88?C) and then stabilize when thermostat opens. At normal operating temperature, signal voltage at control module terminal should be 1.5-2.0 volts. Check sensor for shifted calibration by using sensor TEMPERATURE-TO-RESISTANCE VALUES table. When Code 14 is set, control module will turn on electric cooling fan(s) if equipped.
Chevrolet Corvette ZR-1 1993 CODE 14 ECM TERMINAL & CIRCUIT WIRING IDENTIFICATION
Application ECM Terminal Wire Color CTS Signal A13 Yellow CTS Ground B18 Black
Chevrolet Corvette ZR-1 1993 TEMPERATURE-TO-RESISTANCE VALUES (1)
Temperature ?F (?C) Ohms 210 (100) 185 160 (70) 450 100 (38) 1800 70 (20) 3400 20 (-7) 13,500 0 (-18) 25,000 -40 (-40) 100,700
(1) Measure resistance across sensor terminals.
Chevrolet Corvette ZR-1 1993 - CODE 15 - COOLANT TEMPERATURE SENSOR (SIGNAL VOLTAGE HIGH)
NOTE: Test numbers refer to numbers on diagnostic chart.
- Code 15 indicates control module has seen high resistance in coolant sensor circuit. This could be due to high resistance (cold temperature) or high voltage at coolant sensor terminal at control module for a precalibrated period of time. This checks if conditions for Code 15 still exist.
- This test simulates a low voltage condition. If control module recognizes low voltage signal, scan tester will display greater than 130?C. This indicates control module and wiring are not at fault.
- This test determines if coolant sensor ground or signal circuit is open.
Chevrolet Corvette ZR-1 1993 - Diagnostic Aids
After engine is started, temperature should rise steadily to about 190?F (88?C) and then stabilize when thermostat opens. At normal operating temperature, voltage at control module sensor signal line should be 1.5-2.0 volts. Check sensor for shifted calibration by using sensor TEMPERATURE-TO-RESISTANCE VALUES table. When Code 14 is set, control module will turn on electric cooling fan(s) if equipped.
Chevrolet Corvette ZR-1 1993 CODE 15 ECM TERMINAL & CIRCUIT WIRING IDENTIFICATION
Application ECM Terminal Wire Color CTS Signal A13 Yellow CTS Ground B18 Black
Chevrolet Corvette ZR-1 1993 TEMPERATURE-TO-RESISTANCE VALUES (1)
Temperature ?F (?C) Ohms 210 (100) 185 160 (70) 450 100 (38) 1800 70 (20) 3400 20 (-7) 13,500 0 (-18) 25,000 -40 (-40) 100,700
(1) Measure resistance across sensor terminals.
Chevrolet Corvette ZR-1 1993 - CODE 16 - OPTI-SPARK IGNITION SYSTEM - LOW RESOLUTION PULSE
Ignition system supplies 2 timing inputs to ECM, a high resolution signal (360 pulses per camshaft revolution) and a low resolution signal (8 pulses per camshaft revolution). ECM can determine if either timing input is not being received by comparing inputs. If ECM 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.
- Code 16 will set if 720 high resolution timing pulses occur before any low resolution pulses are detected.
- This step determines if ECM 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 1993 - 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 ECM resolution terminal. If Code 16 does not reset and vehicle still does not start, go to NO START - ENGINE CRANKS OKAY in BASIC TESTING article in this section.
Chevrolet Corvette ZR-1 1993 - CODE 21 - THROTTLE POSITION SENSOR (SIGNAL VOLTAGE HIGH)
NOTE: Test numbers refer to numbers on diagnostic chart.
- This test checks if code is result of a hard failure or an intermittent condition.
- This test simulates a low-voltage condition. If control module recognizes change of state, control module and wiring are okay.
- This step isolates a faulty sensor, control module or open sensor ground circuit. If sensor ground is shared by another sensor, an accompanying code related to that sensor may exist.
Chevrolet Corvette ZR-1 1993 - Diagnostic Aids
A scan tester displays throttle position in volts. Closed throttle voltage should be low. Voltage should increase gradually to about 4.5 volts at a steady rate as throttle angle is increased. If code is intermittent, see INTERMITTENTS in TESTS W/O CODES article in this section.
Chevrolet Corvette ZR-1 1993 CODE 21 ECM TERMINAL & CIRCUIT WIRING IDENTIFICATION
Application ECM Terminal Wire Color TPS Signal C3 Dark Blue TPS Ground B18 Black TPS Reference C2 Gray
Chevrolet Corvette ZR-1 1993 - CODE 22 - THROTTLE POSITION SENSOR (SIGNAL VOLTAGE LOW)
NOTE: Test numbers refer to numbers on diagnostic chart.
- This test checks if code is result of a hard failure or an intermittent condition.
- This test simulates conditions for a Code 21. If control module recognizes change of state, control module and wiring are okay.
- This simulates a high signal voltage to check for an open in TPS signal line to control module. Scan tester should recognize this signal and display high TPS voltage.
Chevrolet Corvette ZR-1 1993 - Diagnostic Aids
A scan tester displays throttle position in volts. Closed throttle voltage should be low. Voltage should increase gradually to about 4.5 volts at a steady rate as throttle angle is increased. If code is intermittent, see INTERMITTENTS in TESTS W/O CODES article in this section.
Chevrolet Corvette ZR-1 1993 CODE 22 ECM TERMINAL & CIRCUIT WIRING IDENTIFICATION
Application ECM Terminal Wire Color TPS Signal C3 Dark Blue TPS Ground B18 Black TPS Reference C2 Gray
Chevrolet Corvette ZR-1 1993 - CODE 23 - MAT SENSOR (SIGNAL VOLTAGE HIGH)
NOTE: Test numbers refer to numbers on diagnostic chart.
- This checks if code is result of a hard failure or an intermittent condition. Code 23 will set if engine has been running for a precalibrated period of time, has reached operating temperature and signal voltage indicates a intake air temperature less than -22?F (-30?C).
- This simulates conditions for a Code 25. If scan tester displays a high temperature, control module and wiring are not at fault.
- This checks for continuity of sensor signal and ground circuits. If ground circuit is shared by other sensors and ground circuit is open, accompanying codes related to those sensors may be present.
Chevrolet Corvette ZR-1 1993 - Diagnostic Aids
If engine is allowed to cool overnight, coolant and MAT sensor values should be close to each other when measured by scan tester. Code 23 will result if signal and ground circuits become open. Check sensor for shifted calibration by using sensor TEMPERATURE-TO-RESISTANCE VALUES table.
Chevrolet Corvette ZR-1 1993 CODE 23 ECM TERMINAL & CIRCUIT WIRING IDENTIFICATION
Application ECM Terminal Wire Color MAT Signal C22 Tan MAT Ground B3 Black
Chevrolet Corvette ZR-1 1993 TEMPERATURE-TO-RESISTANCE VALUES (1)
Temperature ?F (?C) Ohms 210 (100) 185 160 (70) 450 100 (38) 1800 70 (20) 3400 20 (-7) 13,500 0 (-18) 25,000 -40 (-40) 100,700
(1) Measure resistance across sensor terminals.
Chevrolet Corvette ZR-1 1993 - CODE 24 - VEHICLE SPEED SENSOR
Speed sensor, which is a Permanent Magnet (PM) generator, provides control module with vehicle speed information. PM generator, mounted in transmission, produces a pulsing AC voltage signal whenever vehicle speed is greater than 3 MPH. Voltage level and pulses increase with vehicle speed. Control module converts pulsing voltage to MPH, which is used by control module to calculate vehicle adjustments.
NOTE: Test numbers refer to numbers on diagnostic chart.
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 3 MPH.
- Before replacing control module, PROM/MEM-CAL should be checked for correct application.
Chevrolet Corvette ZR-1 1993 - Diagnostic Aids
A faulty or misadjusted park/neutral switch may set a false Code 24. Use scan tester to check for proper signal in Drive while wiggling shifter. Code 24 may set if vehicle is power braked (brakes applied and throttle depressed) for more than 10 seconds.
Chevrolet Corvette ZR-1 1993 - CODE 25 - MAT SENSOR (SIGNAL VOLTAGE LOW)
NOTE: Test numbers refer to numbers on diagnostic chart.
- This checks if code is hard failure or intermittent condition. Code 25 will set if a MAT temperature greater than 266?F (130?C) is sensed for more than a precalibrated period.
- This simulates condition for Code 23. If control module recognizes open circuit and scan tester displays temperature of less than -30?C, control module and wiring are okay.
Chevrolet Corvette ZR-1 1993 - Diagnostic Aids
If engine is allowed to cool overnight, coolant temperature sensor and MAT sensor values should be close to each other when measured by a scan tester. A Code 25 will result if sensor signal circuit is shorted to ground. Check sensor for shifted calibration by using sensor TEMPERATURE-TO-RESISTANCE VALUES table.
Chevrolet Corvette ZR-1 1993 CODE 25 ECM TERMINAL & CIRCUIT WIRING IDENTIFICATION
Application ECM Terminal Wire Color MAT Signal C22 Tan MAT Ground B3 Black
Chevrolet Corvette ZR-1 1993 TEMPERATURE-TO-RESISTANCE VALUES (1)
Temperature ?F (?C) Ohms 210 (100) 185 160 (70) 450 100 (38) 1800 70 (20) 3400 20 (-7) 13,500 0 (-18) 25,000 -40 (-40) 100,700
(1) Measure resistance across sensor terminals.
Chevrolet Corvette ZR-1 1993 - CODE 26 - QUAD-DRIVER NO. 1 ERROR
ECM controls most components with electronic switches completing a ground circuit when actuated. Switches are arranged in groups of 4, called Quad-Driver Modules (QDMs), which can independently control up to 4 outputs (control module terminals). When an output is actuated, terminal is grounded and its voltage normally will be low. When an output is off, its terminal voltage will normally be high.
QDMs are fault-protected. If a relay or solenoid coil is shorted (having very low resistance) or if control side of circuit is shorted to voltage, too much current would be allowed into QDM. QDM senses this and turns driver off or QDM's internal resistance increases to limit current flow and protect QDM. Result is high output terminal voltage when it should be low. If circuit from battery voltage or component is open or control side of circuit is shorted to ground, terminal voltage will be low, even when output is turned off. Either of these conditions is considered to be a QDM fault.
Each QDM has a separate fault line to indicate presence of a current fault to control module central processor. A scan tester displays status of each of these fault lines as "low equals okay" or "high equals fault".
NOTE: Test numbers refer to numbers on diagnostic chart.
- Code 26 will set if the ECM detects the wrong voltage potential for 20 seconds. This test will begin to determine if the QDM-connected air pump relay can be controlled by the ECM. If the relay appears to operate but the air pump does not turn, diagnose mechanical/electrical portions of air pump.
- 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. If a QDM circuit check is done on a relay, it is important to identify and test the relay coil terminals of the harness connector to avoid improper diagnosis. See DRIVE CIRCUIT TEST in CODE 28, QUAD DRIVER NO. 3 ERROR.
Chevrolet Corvette ZR-1 1993 - Diagnostic Aids
Engine should be idling while monitoring QDM status. Using scan tester, monitor QDM status while moving related harness connectors, including ECM harness. If the failure is induced, a fault will status while moving related harness connectors, including ECM harness. If the failure is induced, a fault will appear on scan tester. This can help to isolate intermittent problems. If code persists with no apparent problems, replace ECM.
Chevrolet Corvette ZR-1 1993 - CODE 27 - QUAD-DRIVER NO. 2 ERROR (5.7L "Y" BODY)
ECM uses Quad-Driver Modules (QDMs) to control several devices. When ECM is commanding a component on, voltage of output circuit will be low (near zero volts). When ECM is commanding component off, voltage of output circuit will be high (near battery voltage). Primary function of quad-driver module is to control ground circuit for component being activated. ECM has an internal fault line for each quad-driver module. Fault line status can be displayed on a scan tester. If ECM detects an output voltage other than what is expected on fault line, ECM will set Code 27; however, ECM will not turn on SERVICE ENGINE SOON light.
NOTE: Test numbers refer to numbers on diagnostic chart.
- Code 27 will set if ECM detects wrong voltage on fault line for 3 seconds. This step helps determine which QDM-driven component may have set Code 27.
- This step helps check for a partially shorted coil which would cause excessive current draw. Excessive current draw will be detected on fault line and set this code. If excessive current draw is present, check circuit, and replace defective wiring or component.
- This step will help determine if problem is related to component, wiring or ECM.
Chevrolet Corvette ZR-1 1993 - Drive Circuit Test
To verify drive circuit is operational, turn ignition off. Disconnect component connector. Turn ignition on, and ground ALDL test terminal "B". Probe drive circuit terminal of harness using a test light connected to battery voltage. If test light does not glow, backprobe appropriate terminal at ECM connector. If test light now glows, repair open in circuit between ECM connector and component harness connector. If test light does not glow, problem is faulty ECM connection or faulty ECM.
Chevrolet Corvette ZR-1 1993 - Diagnostic Aids
Using a scan tester, monitor QDM status while moving related harness connectors, including ECM harness. If a failure is induced, a fault will appear on scan tester. If code reappears and no faults can be found, replace ECM.
Chevrolet Corvette ZR-1 1993 - CODE 28 - QUAD-DRIVER NO. 3 ERROR
ECM uses Quad-Driver Modules (QDMs) to control several devices. When ECM is commanding a component on, voltage of output circuit will be low (near zero volts). When ECM is commanding component off, voltage of output circuit will be high (near battery voltage). Primary function of quad-driver module is to control ground circuit for component being activated. ECM has an internal fault line for each quad-driver module. Fault line status can be displayed on a scan tester. If ECM detects an output voltage other than what is expected on fault line, ECM will set Code 28; however, ECM will not turn on SERVICE ENGINE SOON light.
NOTE: Test numbers refer to numbers on diagnostic chart.
- Code 28 will set if ECM detects wrong voltage on fault line for 3 seconds. This step helps determine which QDM-driven component may have set Code 28.
- This step helps check for a partially shorted coil which would cause excessive current draw. Excessive current draw will be detected on fault line and set this code. If excessive current draw is present, check circuit, and replace defective wiring or component.
- This step will help determine if problem is related to component, wiring or ECM.
Chevrolet Corvette ZR-1 1993 - Drive Circuit Test
To verify drive circuit is operational, turn ignition off. Disconnect component connector. Turn ignition on, and ground ALDL test terminal "B". Probe drive circuit terminal of harness using a test light connected to battery voltage. If test light does not glow, backprobe appropriate terminal at ECM connector. If test light now glows, repair open in circuit between ECM connector and component harness connector. If test light does not glow, problem is faulty ECM connection or faulty ECM.
Chevrolet Corvette ZR-1 1993 - Diagnostic Aids
Using a scan tester, monitor QDM status while moving related harness connectors, including ECM harness. If a failure is induced, a fault will appear on scan tester. If code reappears and no faults can be found, replace ECM.
Chevrolet Corvette ZR-1 1993 - CODE 32 - EGR SYSTEM ERROR
EGR vacuum is regulated by an ECM-controlled, normally closed solenoid. ECM will turn EGR on and off (duty cycle) by grounding and ungrounding solenoid drive circuit. Duty cycle is calculated by ECM based on coolant temperature, airflow and engine RPM. ECM will check EGR operation when vehicle speed is greater than 50 MPH, MAP is within calibrated range, throttle angle is 8-30 percent and throttle angle is constant. With ignition on and engine stopped, EGR solenoid is de-energized. Grounding ALDL test terminal should energize solenoid, allowing vacuum to pass through to EGR valve.
NOTE: Test numbers refer to numbers on diagnostic chart.
- To check for plugged intake passage, turn ignition off. Remove EGR valve from intake. Plug exhaust side passage with a suitable stopper. With intake side open, attempt to start engine. If engine runs at a very high idle (up to 3000 RPM is possible) or starts and stalls, EGR intake passage is not plugged. If engine starts and idles normally, intake passage is plugged. To check for plugged exhaust passage, with EGR valve still removed, plug intake passage with a suitable stopper. Start engine. If no exhaust gas is present, passage is plugged.
- By grounding ALDL test terminal "B", EGR solenoid should energize, allowing vacuum to pass through solenoid. Vacuum may slowly bleed off. What is important is that vacuum passes through solenoid.
- When the ALDL test terminal "B" is ungrounded, vacuum should bleed off through a vent in the solenoid valve. What is important is that vacuum no longer exists on EGR side of solenoid.
- This test will determine if the electrical control part of the system is at fault or if the connector or solenoid valve is at fault.
Fig. 27: Chevrolet Corvette ZR-1 1993 - Component Locations - Code 32 Flow Chart EGR System Error
Chevrolet Corvette ZR-1 1993 - CODE 33 - MAP SENSOR (SIGNAL VOLTAGE HIGH)
NOTE: Test numbers refer to numbers on diagnostic chart.
- This test confirms Code 33 and determines if it is result of a hard failure or an intermittent condition. Code 33 will set when voltage signal reading is too high for greater than a precalibrated period of time, TPS voltage indicates throttle is closed and neither Code 21 nor 22 is present.
- This step simulates conditions for a Code 34. If control module recognizes and sets Code 34, low MAP signal, control module and 5-volt reference and MAP signal circuits are not at fault. If ground circuit is shared with other sensors and ground circuit becomes open, additional codes related to these sensors may be set.
Chevrolet Corvette ZR-1 1993 - Diagnostic Aids
With ignition switch in ON position and engine stopped, manifold pressure is equal to atmospheric pressure and signal voltage will be high. Comparison of BARO readings from a known good vehicle using same sensor is a good way to check accuracy of suspect sensor. Readings should be same within .4 volt. Code 33 will result if ground circuit is open, MAP signal circuit is shorted to voltage or to 5-volt reference circuit.
Chevrolet Corvette ZR-1 1993 CODE 33 ECM TERMINAL & CIRCUIT WIRING IDENTIFICATION
Application ECM Terminal Wire Color MAP Signal C21 Light Green MAP Ground B3 Black MAP Reference C7 Gray
Chevrolet Corvette ZR-1 1993 - CODE 34 - MAP SENSOR (SIGNAL VOLTAGE LOW)
NOTE: Test numbers refer to numbers on diagnostic chart.
- This confirms Code 34 and determines if code was caused by a hard failure or an intermittent fault. Code 34 will set when ignition is on and MAP signal voltage is low. On some systems, engine must be running to set code.
- Jumpering MAP signal to 5-volt reference at MAP harness connector will determine if sensor is at fault or if a problem exists with control module or wiring.
- Scan tester may not display 12 volts. Control module recognizes voltage as greater than 4 volts (high MAP voltage signal), indicating control module and MAP signal circuit are not at fault.
Chevrolet Corvette ZR-1 1993 - Diagnostic Aids
With ignition switch in ON position and engine stopped, manifold pressure is equal to atmospheric pressure and signal voltage will be high. Comparing BARO readings with a known good vehicle using same sensor is a good way to check accuracy of suspect sensor. Readings should be same within .4 volt. A Code 34 will also result if 5-volt reference and MAP signal circuits are open or shorted to ground.
Chevrolet Corvette ZR-1 1993 CODE 34 ECM TERMINAL & CIRCUIT WIRING IDENTIFICATION
Application ECM Terminal Wire Color MAP Signal C21 Light Green MAP Ground B3 Black MAP Reference C7 Gray
Chevrolet Corvette ZR-1 1993 - CODE 35 - IAC IDLE SPEED ERROR WITHOUT TECH 1
Code 35 will set when closed throttle engine speed is 150 RPM greater or less than correct idle speed for 20 seconds.
NOTE: Test numbers refer to numbers on diagnostic chart.
- IAC driver is used to extend and retract IAC valve. Movement is verified by an engine speed change. If no change in speed occurs, valve can be retested when removed from throttle body.
- Checks IAC movement quality from step 1). Between 700-1500 RPM, engine speed should change smoothly with each flash of tester light in both extend and retract. If IAC valve is retracted beyond control range (about 1500 RPM), many flashes in extend position may occur before engine speed begins to drop. This is normal on certain engines. Fully extending IAC may cause engine to stall. This may be normal.
- Steps 1) and 2) verified proper IAC valve operation, while this step checks IAC circuits. Each light on node light should flash Red and Green while IAC valve is cycled. While sequence of color is not important, check circuits for faults beginning with poor terminal contacts if either light is off or does not flash Red and Green.
NOTE: For IAC reset procedure, see IDLE SPEED & MIXTURE in ADJUSTMENTS article in this section.
Chevrolet Corvette ZR-1 1993 - Diagnostic Aids
A slow, unstable idle may be caused by a system problem which cannot be overcome by IAC. Scan counts will be greater than 60 if idle is too low and zero counts if idle is too high. If idle is too high, stop engine. Fully extend IAC using driver. Start engine. If idle speed is greater than 800 RPM, look for possible vacuum leaks.
Chevrolet Corvette ZR-1 1993 - System Too Lean
If air/fuel ratio is too lean, idle speed may be either too high (check for vacuum leaks) or too low. Engine speed may vary up and down; disconnecting IAC may not help. Scan tester and/or digital voltmeter (10-megohm) will read an oxygen (O2) sensor output less than 300 mV (.3 volt). Check for low fuel pressure or water in fuel. A contaminated O2 sensor (caused by silicone) will produce lean air/fuel mixtures with an O2 sensor output fixed greater than 800 mV (.8 volt). This may also set Code 45.
Chevrolet Corvette ZR-1 1993 - System Too Rich
If air/fuel ratio is too rich, idle speed will be too low and scan tester counts will usually be greater than 80. System may be obviously rich, with Black smoke from exhaust pipe. Scan tester and/or voltmeter will read an O2 sensor voltage signal fixed greater than 800 mV (.8 volt). Look for high fuel pressure and injectors leaking or sticking. Remove IAC, and inspect bore for foreign material and evidence of IAC valve dragging bore.
Chevrolet Corvette ZR-1 1993 - Throttle Body
Remove IAC, and inspect bore for evidence of IAC valve dragging.
Chevrolet Corvette ZR-1 1993 - IAC Valve Connections
Inspect carefully for loose or corroded connections.
Chevrolet Corvette ZR-1 1993 - PCV Valve
An incorrect PCV valve may cause incorrect idle speed.
Chevrolet Corvette ZR-1 1993 - CODE 35 - IAC IDLE SPEED ERROR USING TECH I
Code 35 will set when closed throttle engine speed is 150 RPM greater or less than correct idle speed for 20 seconds.
NOTE: Test numbers refer to numbers on diagnostic chart.
- Tech 1 RPM control mode is used to extend and retract IAC valve. Movement is verified by an engine speed change. If no change in speed occurs, valve can be retested when removed from throttle body. If IAC valve is retracted beyond control range (about 1500 RPM), many flashes in extend position may occur before engine speed begins to drop. This is normal on certain engines. Fully extending IAC may cause engine to stall. This may be normal.
- This test uses Tech 1 to command IAC-controlled idle speed. Control module issues commands to obtain requested idle speed. Each light on node light should flash Red and Green while IAC valve is cycled. While sequence of color is not important, check circuits for faults beginning with poor terminal contacts if either light is off or does not flash Red and Green.
Chevrolet Corvette ZR-1 1993 - Diagnostic Aids
A slow, unstable idle may be caused by a system problem which cannot be overcome by IAC. Scan counts will be greater than 60 if idle is too low and zero counts if idle is too high. If idle is too high, stop engine. Fully extend IAC with driver. Start engine. If idle speed is greater than 800 RPM, look for possible vacuum leaks.
Chevrolet Corvette ZR-1 1993 - System Too Lean
If air/fuel ratio is too lean, idle speed may be either too high (check for vacuum leaks) or too low. Engine speed may vary up and down; disconnecting IAC may not help. Scan and/or digital voltmeter (10-megohm) will read an oxygen (O2) sensor output less than 300 mV (.3 volt). Check for low fuel pressure or water in fuel. A contaminated O2 sensor (caused by silicone) will produce lean air/fuel mixtures with an O2 sensor output fixed greater than 800 mV (.8 volt). This may also set Code 45.
Chevrolet Corvette ZR-1 1993 - System Too Rich
If air/fuel ratio is too rich, idle speed will be too low and scan tester counts will usually be greater than 80. System may be obviously rich, with Black smoke from exhaust pipe. Scan tester and/or voltmeter will read an O2 sensor voltage signal fixed greater than 800 mV (.8 volt). Look for high fuel pressure and injectors leaking or sticking. Remove IAC, and inspect bore for foreign material and evidence of IAC valve dragging bore.
Chevrolet Corvette ZR-1 1993 - Throttle Body
Remove IAC, and inspect bore for evidence of IAC valve dragging.
Chevrolet Corvette ZR-1 1993 - IAC Valve Connections
Inspect carefully for loose or corroded connections.
Chevrolet Corvette ZR-1 1993 - PCV Valve
An incorrect PCV valve may cause incorrect idle speed.
Chevrolet Corvette ZR-1 1993 - CODE 36 - OPTI-SPARK IGNITION SYSTEM (HIGH RESOLUTION PULSE)
Ignition system supplies 2 timing inputs to ECM, a high resolution signal (360 pulses per camshaft revolution) and a low resolution signal (8 pulses per camshaft revolution). ECM can determine if either timing input is not being received by comparing inputs. If ECM 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 ECM 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 1993 - 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 ECM 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 1993 - CODE 41 - OPTI-SPARK IGNITION SYSTEM (OPEN OR SHORTED EST
Ignition system provides 2 timing inputs to ECM, high resolution (360 pulses per camshaft revolution) and low resolution (8 pulses per camshaft revolution). ECM uses these 2 inputs to determine individual spark timing for each cylinder. Once ECM 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, ECM will disable fuel injectors to prevent flooding of engine.
NOTE: Test numbers refer to numbers on diagnostic chart.
- Code 41 will set if EST circuit voltage exceeds 4.6 volts and engine speed is less than 1500 RPM.
- Without engine running or cranking, voltage would not be present on EST line.
- This step determines if EST signal from ECM 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 1993 - Diagnostic Aids
Because coil driver gets its power from coil, check ignition feed circuit to ignition coil for opens.
Chevrolet Corvette ZR-1 1993 - CODE 42 - EST CIRCUIT GROUNDED
Ignition system provides 2 timing inputs to ECM, high resolution (360 pulses per camshaft revolution) and low resolution (8 pulses per camshaft revolution). ECM uses these 2 inputs to determine individual spark timing for each cylinder. Once ECM 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.
- Code 42 will set if engine speed is less than 3000 RPM and voltage on EST circuit is less than about .5 volt. If engine starts at this point, code is intermittent.
- This test checks for an EST signal from ECM 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.
- A Code 42 will set if high and low resolution circuits are shorted to each other. Before replacing any components, ensure these circuits are not shorted.
Chevrolet Corvette ZR-1 1993 - CODE 43 - ESC ERROR (WITHOUT ESC MODULE)(5.7L "Y" BODY)
The knock sensor informs the ECM of engine detonation. The ECM 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 ECM to be pulled low to about 1.5 volts. Any AC voltage produced by the sensors will travel to the ECM 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 ECM, both sensor circuits become open, resulting in a reference voltage greater than 4.1 volts being seen by the ECM, or one or both circuits become grounded, resulting in a low (less than .78 volt) reference voltage being seen by ECM.
NOTE: Test numbers refer to numbers on diagnostic chart.
- If an audible knock is heard from the engine, repair the internal engine problem, as normally no knock should be detected at idle. The ECM supplies 5 volts on the knock sensor circuit which should be present at the knock sensor terminals when the sensors are disconnected.
- This test will determine if the knock sensor is faulty or if the PROM is faulty.
- An improperly installed sensor can prevent the knock sensor from grounding to the block.
Chevrolet Corvette ZR-1 1993 - Diagnostic Aids
The ECM 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 proper PROM is installed in ECM.
Chevrolet Corvette ZR-1 1993 - CODE 44 - LEAN EXHAUST INDICATION
NOTE: The 5.7L (VIN P) engine is equipped with 2 oxygen sensors. On these models, Code 44 will set if the left sensor circuit is lean. Code 64 will set if the right sensor circuit is lean. Use this chart for Code 64 also and perform tests for applicable sensor.
O2 sensor acts like an open sensor circuit and produces no voltage when exhaust temperature is less than 600?F (316?C). An open sensor circuit or cold sensor causes "open loop" operation. Corvette is equipped with 2 oxygen sensors. Code 44 will reflect a lean left O2 sensor; Code 64 will indicate a lean right O2 sensor. Perform test procedures for right or left sensor as necessary.
NOTE: Test number refers to number on diagnostic chart.
- Checks to see if O2 sensor is registering a lean condition. Code 44 is set when O2 sensor voltage signal at control module is low (less than .3 volt) for a precalibrated period and system is operating in "closed loop".
Chevrolet Corvette ZR-1 1993 - Diagnostic Aids
Using scan tester, observe Block Learn Memory (BLM) value at different RPMs. If conditions for a Code 44 exist, block learn value will be about 150.
Chevrolet Corvette ZR-1 1993 - O2 Sensor Wire
O2 sensor wire may be mispositioned and laying against exhaust manifold. Check for ground between sensor and wire connector.
Chevrolet Corvette ZR-1 1993 - Fuel Contamination
Water, even small amounts, near in-tank fuel pump inlet can be delivered to injector. Water may cause a lean exhaust and set Code 44.
Chevrolet Corvette ZR-1 1993 - Fuel Pressure
System will be lean if fuel pressure is low. If necessary, monitor fuel pressure while driving vehicle. For fuel pressure checking procedure, see BASIC TESTING article in this section.
Chevrolet Corvette ZR-1 1993 - Exhaust Leaks
If exhaust system has large leaks, exhaust system negative pressure pulses can cause outside air to be drawn into system and past O2 sensor. Vacuum or crankcase leaks can also cause a lean condition.
Chevrolet Corvette ZR-1 1993 - Misfire Or Stall
If engine misfires or stalls (including running out of fuel) while vehicle is moving, a Code 44 may set. If Code 44 is intermittent, see INTERMITTENTS in TESTS W/O CODES article in this section.
Chevrolet Corvette ZR-1 1993 CODE 44 ECM TERMINAL & CIRCUIT WIRING IDENTIFICATION
Application ECM Terminal Wire Color 5.7L "Y" Body Left O2 Signal D6 Purple Left O2 Ground D17 Tan Right O2 Signal D22 Purple Right O2 Ground D17 Tan
Chevrolet Corvette ZR-1 1993 - CODE 45 - RICH EXHAUST INDICATION
NOTE: The 5.7L (VIN P) engine is equipped with 2 oxygen sensors. On these models, Code 45 will set if the left sensor circuit is rich. Code 65 will set if the right sensor circuit is lean. Use this chart for Code 65 also and perform tests for applicable sensor.
O2 sensor acts like an open sensor circuit and produces no voltage when exhaust temperature is less than 600?F (316?C). An open sensor circuit or cold sensor causes "open loop" operation. Code 45 indicates a rich exhaust. Diagnosis should begin with fuel pressure, leaking injector, HEI shielding (ground), vapor canister fuel saturation, coolant sensor, MAP sensor, O2 sensor contamination and TPS intermittent output.
Corvette is equipped with 2 oxygen sensors. Code 45 will reflect a rich left O2 sensor; Code 65 will indicate a rich right O2 sensor. Perform test procedures for right or left sensor as necessary.
NOTE: Test number refers to number on diagnostic chart.
- Test checks to see if O2 sensor is registering a rich condition. Code 45 is set when vehicle is at operating temperature (in "closed loop"), throttle angle is greater than idle, O2 sensor signal at control module is greater than .7 volt for a precalibrated period and time since engine start is one minute or more.
Chevrolet Corvette ZR-1 1993 - Diagnostic Aids
If other codes of lower number are set with Code 45, use those charts first. Malfunction in MAP or TPS sensor circuits can cause a Code 45 to set. If other codes are not set, Code 45, rich exhaust, is most likely caused by:
Chevrolet Corvette ZR-1 1993 - Fuel Pressure High
If fuel pressure is too high, air/fuel ratio will be rich. For fuel pressure checking procedure, see BASIC TESTING article in this section. Control module can compensate for slight increases, but a Code 45 will be set if air/fuel ratio becomes too rich.
Chevrolet Corvette ZR-1 1993 - Ignition Ground
If an open occurs on HEI ground circuit, HEI induced electrical "noise" may result, causing simulated reference pulses to be picked up by control module on reference line of EST harness. Additional pulses result in a higher than actual engine speed signal. Control module will increase injector pulse width ("on" time) to match increased RPM signal. Scan tester will show higher than actual RPM, which can help in diagnosing this problem.
Chevrolet Corvette ZR-1 1993 - Evaporative Fuel Canister
Fuel saturation of charcoal canister will cause a rich air/fuel ratio. If canister is full of fuel, check canister control valves and hoses.
Chevrolet Corvette ZR-1 1993 - MAP Sensor
An output causing control module to sense a higher than normal manifold pressure (low vacuum) can cause system to go rich. Disconnecting MAP sensor will allow control module to substitute a fixed value for MAP sensor. If condition disappears, substitute a different MAP sensor, and continue testing.
Chevrolet Corvette ZR-1 1993 - TPS
An intermittent TPS output will cause system to operate rich due to a false indication of engine acceleration.
Chevrolet Corvette ZR-1 1993 - O2 Sensor Contamination
O2 sensor contamination, caused by silicone in certain fuels or use of improper RTV sealant, may cause a White powdery coating to cover exterior of O2 sensor. False high signal voltage (low oxygen content sensed) produced is interpreted by control module as a rich mixture, causing control module to set Code 45.
Chevrolet Corvette ZR-1 1993 - EGR Problem
EGR valve sticking open at idle is usually accompanied by a rough idle and/or stalling.
Also check for shorted or leaking injector and fuel-contaminated oil. If Code 45 is intermittent, see INTERMITTENTS in TESTS W/O CODES article in this section.
Chevrolet Corvette ZR-1 1993 CODE 45 ECM TERMINAL & CIRCUIT WIRING IDENTIFICATION
Application ECM Terminal Wire Color 5.7L "Y" Body Left O2 Signal D6 Purple Left O2 Ground D17 Tan Right O2 Signal D22 Purple Right O2 Ground D17 Tan
Chevrolet Corvette ZR-1 1993 - CODE 51 - FAULTY PROM/MEM-CAL
Ensure all pins are fully inserted in socket. If pins are okay, replace PROM/MEM-CAL, clear memory and recheck. If Code 51 reappears, replace control module.
Chevrolet Corvette ZR-1 1993 - CODE 52 - FAULTY CAL-PAK
Ensure all pins are fully inserted in socket. If pins are okay, replace CAL-PAK, clear memory and recheck. If Code 51 reappears, replace control module.
Chevrolet Corvette ZR-1 1993 - CODE 52 - LOW ENGINE OIL TEMPERATURE (5.7L "Y" BODY)
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 ECM will see a high monitored voltage signal on engine oil temperature sensor signal terminal. As temperature increases, resistance decreases and ECM 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 ECM and wiring are okay.
- Determines if engine oil temperature signal or sensor ground circuit is open.
Chevrolet Corvette ZR-1 1993 - 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 1993 - CODE 53 - SYSTEM OVERVOLTAGE
This code indicates a basic charging system problem. Code 53 will set when voltage at control module terminal is greater or less than specification for a precalibrated time. If voltage at ECM battery voltage terminal is not within specification, check and repair charging system.
Chevrolet Corvette ZR-1 1993 CHARGING SYSTEM SPECIFICATIONS
Application Minimum Charge Maximum Charge 5.7L 9.6 16.0
Fig. 50: Chevrolet Corvette ZR-1 1993 - Component Locations - Code 53 Flow Chart System Overvoltage
Chevrolet Corvette ZR-1 1993 - CODE 55 - FUEL LEAN MONITOR
ECM is capable of determining if fuel system can deliver adequate fuel during power enrichment (heavy acceleration). During power enrichment conditions, ECM 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 ECM 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 1993 - 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. 51: Chevrolet Corvette ZR-1 1993 - Component Locations - Code 55 Schematic Fuel Lean Monitor
Fig. 52: Chevrolet Corvette ZR-1 1993 - Component Locations - Code 55 Flow Chart Fuel Lean Monitor
Chevrolet Corvette ZR-1 1993 - CODE 62 - HIGH ENGINE OIL TEMPERATURE (5.7L "Y" BODY)
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 ECM will see a high monitored voltage signal on engine oil temperature sensor circuit. As temperature increases, resistance decreases and ECM 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 1993 - 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. 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 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 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 1993 - CODE 63 - RIGHT OXYGEN SENSOR OPEN
See Code 13 chart and duplicate procedure for right O2 sensor as necessary.
Chevrolet Corvette ZR-1 1993 - CODE 64 - RIGHT OXYGEN SENSOR LEAN
See Code 44 chart and duplicate procedure for right O2 sensor as necessary.
Chevrolet Corvette ZR-1 1993 - CODE 65 - RIGHT OXYGEN SENSOR RICH
See Code 45 chart and duplicate procedure for right O2 sensor as necessary.
Chevrolet Corvette ZR-1 1993 - CODE 66 - A/C PRESSURE SENSOR
A/C pressure sensor responds to changes in A/C refrigerant system high side pressure. ECM uses A/C compressor load input to determine engine idle speed. Sensor uses a 5-volt reference signal from ECM and returns an input signal to ECM on a separate line. Low pressure (zero psi) will return a signal of about .1 volt. High pressure will return a signal of about 4.6 volts.
NOTE: Test numbers refer to numbers on diagnostic chart.
- Checks voltage signal from A/C pressure sensor to ECM.
- Checks to see if high signal is from a shorted sensor or a short to voltage in circuit. Normally, disconnecting sensor would make a normal circuit go to nearly zero volts.
- Checks to see if low voltage signal is from sensor or circuit. Jumpering sensor signal circuit to 5-volt reference checks circuit, connections and ECM.
- Checks to see if low voltage signal was due to an open in sensor circuit; previous step eliminated pressure sensor as a possible cause.
Chevrolet Corvette ZR-1 1993 - Diagnostic Aids
Code 66 sets when signal voltage falls outside normal sensor range and is not due to a A/C system problem. If problem is intermittent, check for opens or shorts in harness and poor connections. If wiring is okay, replace pressure sensor. If code resets, replace ECM.
Fig. 56: Chevrolet Corvette ZR-1 1993 - Component Locations - Code 66 Flow Chart A/C Pressure Sensor
Chevrolet Corvette ZR-1 1993 - CODE 67 - A/C PRESSURE SENSOR (5.7L "Y" BODY)
ECM determines when A/C clutch is engaged by monitoring A/C status line. If A/C pressure does not increase by at least 9 psi when A/C clutch is turned on, Code 67 will set.
NOTE: Test numbers refer to numbers on diagnostic chart.
- Code 67 will set if ECM does not detect a A/C pressure increase of at least 9 psi when A/C clutch is engaged.
- If relay power feed is intermittent, A/C clutch status terminal may not detect voltage when A/C is commanded on.
- If A/C clutch status line becomes intermittently open or shorted while compressor is on, ECM will be wrongly detecting A/C clutch going on and off. When this occurs and clutch remains engaged, ECM will not detect pressure change and a Code 67 will be set.
- If A/C compressor clutch is disconnected or if A/C status circuit is open between splice and clutch, compressor clutch will not engage, but ECM will detect voltage on A/C status line, which will indicate clutch is on. If A/C switch is cycled on and off at this point, no pressure change will be detected and a Code 67 will set.
Chevrolet Corvette ZR-1 1993 - Diagnostic Aids
A Code 67 will store in ECM memory but not turn on SERVICE ENGINE SOON light.
Chevrolet Corvette ZR-1 1993 - CODE 68 - A/C RELAY CIRCUIT SHORTED
When ECM detects A/C has been requested, ECM 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 ECM. If ECM 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, ECM 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 ECM has disengaged A/C relay.
- This step will isolate ignition feed portion of circuit from clutch circuit.
- If Code 68 reappears at this step, ECM is internally shorted to voltage.
Chevrolet Corvette ZR-1 1993 - CODE 69 - A/C COMPRESSOR RELAY
When ECM detects A/C has been requested, ECM will activate the A/C clutch relay. When the relay has been activated, voltage should be present at both the A/C compressor clutch and the A/C clutch status line terminal of the ECM. If the ECM activates the A/C clutch relay but does not detect voltage present at the A/C status terminal for more than 10 seconds, Code 69 will set. An open or short to ground at any point in the A/C status circuit will cause Code 69 to set. A Code 69 fault will be stored in ECM memory but will not turn on the SERVICE ENGINE SOON light.
NOTE: Test numbers refer to numbers on diagnostic chart.
- Code 69 will set if the ECM has commanded the A/C on and no voltage is detected on the A/C status line after 20 seconds.
- If the A/C compressor clutch operates properly and scan tester indicates A/C status off, then an open exists between the ECM and the splice to the compressor.
Chevrolet Corvette ZR-1 1993 - CODE 72 - GEAR SELECTOR SWITCH (5.7L "Y" BODY)
ECM monitors 2nd, 3rd and 4th gear switch status. ECM uses this information to help determine shift points as well as determining TCC apply times. If ECM notes a 3rd gear switch signal without detecting a 2nd gear switch signal, Code 72 will set. An open in 2nd gear switch status circuit will cause this code to set.
NOTE: Test numbers refer to numbers on diagnostic chart.
- Code 72 will set if 2nd gear switch is open, vehicle speed is greater than 30 MPH, TPS is greater than 70 percent, engine speed is greater than 5000 RPM and all conditions have been met for 1 1/2 seconds.
- This step checks operation of 2nd gear switch. When transmission shifts into 2nd gear, scan tester should indicate 2nd gear on.
- Disconnecting TCC connector simulates an open switch to determine if 2nd gear switch circuit is shorted to ground or if a problem exists inside of transmission.
- This step determines if ECM and wiring are okay. Grounding 2nd gear switch circuit should cause scan tester 2nd gear status to display "yes", indicating transmission is in 2nd gear.
Chevrolet Corvette ZR-1 1993 - CODE 85 - PROM ERROR & CODE 87 - EEPROM ERROR
Ensure all ECM connectors are fully inserted in socket. If okay, have ECM reprogrammed using appropriate equipment. If equipment is not available, have ECM serviced through dealership.
Chevrolet Corvette ZR-1 1993 - SUMMARY
If no hard fault codes are present, driveability symptoms exist or intermittent codes exist, proceed to TESTS W/O CODES article in this section for diagnosis by symptom (i.e., ROUGH IDLE, NO START, etc.) or intermittent diagnostic procedures.