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Chevrolet Cavalier Z24 1994 - 1994 ENGINE PERFORMANCE Self-Diagnostics - 2.2L 4-Cyl.
Chevrolet Cavalier Z24 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 Cavalier Z24 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 Cavalier Z24 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 Cavalier Z24 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 Cavalier Z24 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 - 2.2L article in this section below.
- 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 Cavalier Z24 1994 - RETRIEVING CODES (NON-SCAN)
NOTE: On models using a 12-terminal DLC (previously referred to as the ALDL), if a wire is present at terminal "B", inserting a jumper wire into test and ground terminals of DLC 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 the ENGINE PERFORMANCE section. On models not using a 12-terminal DLC or not having a wire present in terminal "B", codes must be retrieved using a hand-held scan tester.
Chevrolet Cavalier Z24 1994 DATA LINK CONNECTOR (DLC) TEST TERMINALS
Application Ground/Test 12-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 appropriate SYSTEM/COMPONENT TESTS - 2.2L article in this section below. 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.
Fig. 1: Chevrolet Cavalier Z24 1994 - Component Locations - ALDL/DLC 12-Pin Connector Terminal ID
Chevrolet Cavalier Z24 1994 - READING TROUBLE CODES
The 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 the SERVICE ENGINE SOON light or by reading digital display on a scan tester. The scan tester is faster to use, more accurate and capable of reading information which otherwise would necessitate the testing of individual control module and/or sensor/solenoid connector terminals using a digital voltmeter. For more information, 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 Cavalier Z24 1994 - TROUBLE CODE DEFINITION
Chevrolet Cavalier Z24 1994 ECM/PCM TROUBLE CODE DEFINITION
Code No. Circuit Affected 12 (1) No RPM Reference Pulse 13 Single Sensor Models Oxygen Sensor Circuit Open Dual Sensor Models Left Oxygen Sensor Circuit Open 14 Coolant Temperature Sensor Signal Voltage Low 15 Coolant Temperature Sensor Signal Voltage High 19 Intermittent 7X Signal 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 27 Or 28 Quad-Driver Error 29 Quad-Driver Error 32 EGR System Error 33 MAP Sensor Signal Voltage High 34 MAP Sensor Signal Voltage Low 35 IAC Idle Speed Error 43 ESC (Knock Sensor) Error 44 Single Sensor Models Lean Exhaust Indication Dual Sensor Models Left Lean Exhaust Indication 45 Single Sensor Models Rich Exhaust Indication Dual Sensor Models Left Rich Exhaust Indication 51 Faulty PROM, MEM-CAL Or ECM/PCM 53 System Overvoltage 55 ECM/PCM Error Fuel Lean Monitor 58 Transmission Fluid Temp. High 59 Transmission Fluid Temp. Low 63 Right Oxygen Sensor Circuit Open (Dual-Sensor Models) 64 Right Oxygen Sensor Lean (Dual-Sensor Models) 65 Single Sensor Models Injector Current Low Dual Sensor Models Right Oxygen Sensor Rich 66 A/C Pressure Sensor 67 A/C Pressure Sensor 79 VSS Signal Voltage High 80 Transmission Component 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).
Chevrolet Cavalier Z24 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. - 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 Cavalier Z24 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 Cavalier Z24 1994 - 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. See COMPONENT LOCATIONS in SYSTEM/COMPONENT TESTS - 2.2L article in this section below.
Chevrolet Cavalier Z24 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 Cavalier Z24 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 Cavalier Z24 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 Cavalier Z24 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 the 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 Cavalier Z24 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 Cavalier Z24 1994 MULTIPORT FUEL INJECTION (MFI)
Tester Position Units Measured Nominal Data 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 A/T RPM Spec. +/-25 RPM in Drive M/T RPM Spec. +/-50 RPM in Neutral 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 Cavalier Z24 1994 - ECM/PCM CODE CHARTS
NOTE: In following diagnostic tests, schematics and illustrations are courtesy of General Motors Corp.
Chevrolet Cavalier Z24 1994 - CODE 13, OPEN OXYGEN SENSOR CIRCUIT
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 Cavalier Z24 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 Cavalier Z24 1994 CODE 13 PCM TERMINAL & CIRCUIT WIRING IDENTIFICATION
Application PCM Terminal Wire Color O2 Signal PA12 Purple O2 Ground PB6 Tan
Chevrolet Cavalier Z24 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.
NOTE: On 2.2L, Code 14 does not differentiate between high or low voltage. If scan on these models indicates coolant temperature less than -30?C, go to Code 15 chart and use yes column. If scan indicates greater than 130?C, use yes column of this code chart. If scan indicates neither high nor low temperature, code is intermittent or sensor is out of calibration. See TEMPERATURE-TO-RESISTANCE VALUES table. - This tests for grounded sensor signal line between control module and coolant sensor.
Chevrolet Cavalier Z24 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 Cavalier Z24 1994 CODE 14 PCM TERMINAL & CIRCUIT WIRING IDENTIFICATION
Application PCM Terminal Wire Color CTS Signal PC10 Yellow CTS Ground PB1 Black
Chevrolet Cavalier Z24 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 Cavalier Z24 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 Cavalier Z24 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 Cavalier Z24 1994 CODE 15 PCM TERMINAL & CIRCUIT WIRING IDENTIFICATION
Application PCM Terminal Wire Color CTS Signal PC10 Yellow CTS Ground PB1 Black
Chevrolet Cavalier Z24 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 Cavalier Z24 1994 - CODE 19, INTERMITTENT 7X SIGNAL
The ignition control module sends a reference signal to the PCM 7 times per crankshaft revolution to indicate crankshaft position and RPM so that the PCM can determine when to pulse the ignition coils and control ignition timing. A 5-volt reference is supplied to the PCM from terminal "G" of the ignition module. This 5-volt reference signal is monitored by the PCM. The ignition module pulls this signal low based upon 7X reference pulses. The seventh pulse is used for crankshaft position (sync) reference. Code 19 is set if the PCM misses at least 20 sync pulses within 4 minutes and 16 seconds.
NOTE: Test numbers refer to numbers on diagnostic chart.
- This step determines if the PCM recognizes a problem. If it doesn't set Code 19 at this point, the problem is intermittent.
- When a 7X resync occurs, engine stumble also occurs. If a component connection or circuitry is at fault, engine stumble may be induced by wiggling the circuit or connection.
Chevrolet Cavalier Z24 1994 - Diagnostic Aids
If vehicle has non-standard electrical equipment (CB radios, 2-way radios, etc.) check to see if their operation may be causing a 7X resync which may set Code 19. If a "cranks but won't start" condition has existed, code may be due to 20 attempted starts without turning off ignition switch.
Chevrolet Cavalier Z24 1994 - CODE 21, THROTTLE POSITION 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 test checks if code is result of a hard failure or an intermittent condition.
NOTE: On 2.2L, Code 21 does not differentiate between high or low voltage. If scan indicates TPS less than .19 volt, go to Code 22 chart and use yes column. If scan indicates TPS greater than 3.9 volts, use yes column of this code chart. If scan indicates TPS is .33-1.33 volts, code is intermittent. See TESTS W/O CODES article in the ENGINE PERFORMANCE section to diagnose intermittent code problems. - 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 Cavalier Z24 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 Cavalier Z24 1994 CODE 21 PCM TERMINAL & CIRCUIT WIRING IDENTIFICATION
Application PCM Terminal Wire Color TPS Signal PB7 Dark Blue TPS Ground PB2 Black TPS Reference PA4 Gray
Chevrolet Cavalier Z24 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 Cavalier Z24 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 Cavalier Z24 1994 CODE 22 PCM TERMINAL & CIRCUIT WIRING IDENTIFICATION
Application PCM Terminal Wire Color TPS Signal PB7 Dark Blue TPS Ground PB2 Black TPS Reference PA4 Gray
Chevrolet Cavalier Z24 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).
NOTE: On 2.2L, Code 23 does not differentiate between high and low voltage. If scan indicates intake air temperature less than -30?C, go to Code 25 chart and use yes column. If scan indicates greater than 130?C, use yes column of this code chart. If scan indicates neither high nor low temperature, code is intermittent or sensor is out of calibration. See TEMPERATURE-TO-RESISTANCE VALUES table. - 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 Cavalier Z24 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 Cavalier Z24 1994 CODE 23 PCM TERMINAL & CIRCUIT WIRING IDENTIFICATION
Application PCM Terminal Wire Color MAT Signal PC9 Tan MAT Ground PB2 Black
Chevrolet Cavalier Z24 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 Cavalier Z24 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.
- 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 Cavalier Z24 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 Cavalier Z24 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 Cavalier Z24 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 Cavalier Z24 1994 CODE 25 PCM TERMINAL & CIRCUIT WIRING IDENTIFICATION
Application PCM Terminal Wire Color MAT Signal PC9 Tan MAT Ground PB2 Black
Chevrolet Cavalier Z24 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 Cavalier Z24 1994 - CODE 26, QUAD-DRIVER ERROR
PCM 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.
- Checks to see if code was set as the result of a current or intermittent condition.
- Checks MIL operation.
Chevrolet Cavalier Z24 1994 - Diagnostic Aids
Tech 1 and other scan testers have the ability to command the MIL and TEMP light on and off. A faulty driver circuit or poor connection can result in setting of Code 26.
Chevrolet Cavalier Z24 1994 - CODE 27, QUAD-DRIVER NO. 1 ERROR
PCM 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". Because of the brake and 3rd gear switches in the TCC circuit, Code 27 will set if QDM No. 1 is high for 20 seconds or more with battery voltage is sensed at greater than 10.5 volts and TCC is commanded on.
Chevrolet Cavalier Z24 1994 - CODE 28, QUAD-DRIVER NO. 2 ERROR
PCM 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". Code 28 will set if QDM No. 2 is high for 20 seconds or more with battery voltage is sensed at greater than 10.5 volts.
Fig. 26: Chevrolet Cavalier Z24 1994 - Component Locations - Code 28 Flow Chart (Cavalier)
Chevrolet Cavalier Z24 1994 - CODE 32, EGR SYSTEM ERROR
A properly operating EGR system will directly affect air/fuel mixture requirements of the engine. Since the exhaust gas introduced into air/fuel mixture contains very little oxygen and can not be used in combustion, less fuel is required to maintain a correct air/fuel ratio. If EGR system were to fail in a closed position, exhaust gas would be replaced with air and air/fuel mixture would be leaner. PCM would compensate for lean condition by adding fuel, resulting in higher long term fuel trim values.
Fuel control is conducted within fuel trim cells. Since EGR is not used at idle, idle cell would not be affected by EGR system operation. Long term fuel trim values in all cells will be close to one another when EGR system is properly functioning. If EGR system is inoperative, long term fuel trim values in open throttle cells would change to compensate for resulting lean or rich mixtures, but values in closed throttle cell would not change.
NOTE: Test numbers refer to numbers on diagnostic chart.
Chevrolet Cavalier Z24 1994 - Plugged Intake Passage
1) Shut off engine, and remove EGR valve. Plug exhaust side port using a shop rag or suitable plug. Attempt to start engine. If engine runs at a very high idle (up to 3000 RPM is possible) or if engine starts and stalls, EGR intake passage is not plugged. If vehicle starts and idles normally, intake side passage is plugged.
Chevrolet Cavalier Z24 1994 - Plugged Exhaust Passage
With EGR valve removed, plug intake manifold side passage using a suitable plug. Start engine and listen for exhaust noise. If no exhaust gas escapes from open EGR port, exhaust passage is plugged.
NOTE: Ensure shop exhaust is not connected during the following steps. DO NOT allow engine to run longer than 15 seconds.
- 2) Remaining test checks ability of EGR valve to interact with exhaust system. System uses a negative backpressure EGR valve which should hold vacuum with engine off.
- 3) When engine is started, exhaust backpressure at base of EGR valve should open valve's internal bleed. This will vent applied vacuum, allowing valve to seat.
Chevrolet Cavalier Z24 1994 - Diagnostic Aids
Check vacuum lines for proper routing.
Fig. 29: Chevrolet Cavalier Z24 1994 - Component Locations - Code 32 Flow Chart (Cavalier)
Chevrolet Cavalier Z24 1994 - CODE 33, MAP SENSOR SIGNAL VOLTAGE HIGH
- 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 Cavalier Z24 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 Cavalier Z24 1994 CODE 33 PCM TERMINAL & CIRCUIT WIRING IDENTIFICATION
Application PCM Terminal Wire Color MAP Signal PB9 Light Green MAP Ground PB2 Purple MAP Reference PA3 Gray
Chevrolet Cavalier Z24 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 Cavalier Z24 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 Cavalier Z24 1994 CODE 34 PCM TERMINAL & CIRCUIT WIRING IDENTIFICATION
Application PCM Terminal Wire Color MAP Signal B7 Light Green MAP Ground D3 Purple MAP Reference C8 Gray
Chevrolet Cavalier Z24 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 Cavalier Z24 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 Cavalier Z24 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 Cavalier Z24 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 Cavalier Z24 1994 - Throttle Body
Remove IAC, and inspect bore for evidence of IAC valve dragging.
Chevrolet Cavalier Z24 1994 - IAC Valve Connections
Inspect carefully for loose or corroded connections.
Chevrolet Cavalier Z24 1994 - PCV Valve
An incorrect PCV valve may cause incorrect idle speed.
Chevrolet Cavalier Z24 1994 - CODE 43, ESC ERROR
NOTE: Test numbers refer to numbers on diagnostic chart. If an audible knock is heard from engine at idle, repair internal engine problems before proceeding.
- If tapping on engine does not produce a knock signal on scan tester, try tapping engine closer to sensor before proceeding.
- PCM supplies a 5-volt reference signal on knock sensor line. With knock sensor connected, this signal is pulled low to about 2.5 volts. Knock signal, which is an AC signal, rides on this 2.5-volt DC signal.
- This test determines if knock sensor is faulty or if ESC portion of MEM-CAL is faulty.
Chevrolet Cavalier Z24 1994 - Diagnostic Aids
Check knock sensor signal circuit for a potential open or short to ground. An open knock signal circuit would cause 5-volt reference to remain high at PCM knock signal terminal. A short to ground in knock signal circuit would cause 5-volt reference signal to pull low to near zero volts. Resistance to ground through knock sensor should be 3300-4500 ohms. Also check for proper installation of MEM-CAL.
Fig. 36: Chevrolet Cavalier Z24 1994 - Component Locations - Code 43 Schematic (Cavalier) ESC Error
Fig. 37: Chevrolet Cavalier Z24 1994 - Component Locations - Code 43 Flow Chart (Cavalier) ESC Error
Chevrolet Cavalier Z24 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 Cavalier Z24 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 Cavalier Z24 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 Cavalier Z24 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 Cavalier Z24 1994 CODE 44 PCM TERMINAL & CIRCUIT WIRING IDENTIFICATION
Application PCM Terminal Wire Color O2 Signal PA12 Purple O2 Ground PB6 Tan
Fig. 40: Chevrolet Cavalier Z24 1994 - Component Locations - Code 44 Flow Chart (Cavalier)
Chevrolet Cavalier Z24 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 Cavalier Z24 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 Cavalier Z24 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 Cavalier Z24 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 Cavalier Z24 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 Cavalier Z24 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 Cavalier Z24 1994 - TPS
An intermittent TPS output will cause system to operate rich due to a false indication of engine acceleration.
Chevrolet Cavalier Z24 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 Cavalier Z24 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 Cavalier Z24 1994 CODE 45 PCM TERMINAL & CIRCUIT WIRING IDENTIFICATION
Application PCM Terminal Wire Color O2 Signal PA12 Purple O2 Ground PB6 Tan
Chevrolet Cavalier Z24 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 Cavalier Z24 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. 45: Chevrolet Cavalier Z24 1994 - Component Locations - Code 55 Flow Chart (Cavalier)
Chevrolet Cavalier Z24 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 4.9 volts. The PCM will disable the compressor clutch if Code 66 is current.
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 or 5-volt reference circuit; previous step eliminated pressure sensor as a possible cause.
Chevrolet Cavalier Z24 1994 - Diagnostic Aids
The 5-volt reference for the TPS is the same 5 volts used by the A/C pressure sensor. If the 5-volt reference has a short to ground, the MAP sensor, A/C pressure sensor and other related sensors will also have a short to ground. This short to ground will not damage the PCM. When the shorted 5-volt reference circuit is repaired, the PCM 5-volt reference will return to normal.
In extremely low temperature climate, the A/C pressure signal can drop as low as .3 volt. If this happens, Code 66 will set and disable the A/C system. Clear code and recheck A/C system in a heated garage to determine if outside ambient temperature is cause for Code 66 setting.
Chevrolet Cavalier Z24 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.