Engine Controls - Tests W/codes - 4.3l Chevrolet Caprice Impala SS

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 appropriate BASIC TESTING article in this section. Failure to do so may result in lost diagnostic time.

If no faults were found while performing BASIC DIAGNOSTIC PROCEDURES, proceed with DIAGNOSTIC PROCEDURE under SELF-DIAGNOSTIC SYSTEM. If no fault codes are 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.

Note. Powertrain Control Module (PCM) may 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 store a numerical code and, in most cases, illuminate SERVICE ENGINE SOON light located on instrument panel. SERVICE ENGINE SOON light is also referred to as the Malfunction Indicator Light (MIL). Malfunctions are recorded as hard failures or as intermittent failures.

Note. Models equipped with OBD II diagnostic systems may have additional diagnostic information and procedures available; however, to fully utilize information and procedures requires the use of a Tech 1 scan tester. See tester owners manual for additional information.

Hard Failures

Most 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 display degraded driveability.

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, 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.

DIAGNOSTIC PROCEDURE

Diagnosis of computerized engine control system should be performed in following order

1. 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»(/chevrolet/caprice-impala-ss/1995-1996/remont/testing-diagnostics/#engine-controls-basic-testing) article in this section.
2. If trouble codes were displayed, 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»(/chevrolet/caprice-impala-ss/1995-1996/remont/testing-diagnostics/#engine-controls-tests-wcodes-43l__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»(/chevrolet/caprice-impala-ss/1995-1996/remont/testing-diagnostics/#engine-controls-tests-wo-codes) article in this section.
3. If no trouble codes are present and a driveability problem exists, refer to SYMPTOMS in «TESTS W/O CODES»(/chevrolet/caprice-impala-ss/1995-1996/remont/testing-diagnostics/#engine-controls-tests-wo-codes) article in this section. Doing so will help identify proper system or component to check in «SYSTEM/COMPONENT TESTS - 4.3L»(/chevrolet/caprice-impala-ss/1995-1996/remont/testing-diagnostics/#engine-controls-systemcomponent-tests-43l) article in this section.
4. After necessary repairs are made, clear trouble codes, verify vehicle will enter "closed loop" operation and ensure code does not reset.

Note. For specific information on retrieving codes using a scan tester, refer to user and reference manuals supplied with tester.

Note. Field service mode check can only be performed on vehicles equipped with 12-pin DLC with a wire present in test terminal "B". See DATA LINK CONNECTOR (DLC) TEST TERMINALS .

DATA LINK CONNECTOR (DLC) TEST TERMINALS

Scheme 3

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 (some models) or by reading digital display on a scan tester. Scan tester is faster to use, more accurate and capable of reading information which otherwise would necessitate testing individual control module and sensor/solenoid connector terminals using a digital voltmeter. See SCAN TESTER USAGE and SCAN DATA .

Note. When using most scan testers, a time delay exists between serial data updates. For instantaneous response, a digital voltmeter must be used.

If scan tester is not available, reading flashes of SERVICE ENGINE SOON light is possible by grounding diagnostic test terminal "B" (if a wire is present) of DLC with ignition on and engine off. (Scheme 3) 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.

TROUBLE CODE DEFINITION

TROUBLE CODE DEFINITION

TROUBLE CODE CONVERSION

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

1. Enter diagnostic mode. Read and record all stored trouble codes. Exit diagnostic mode, and clear trouble codes. See «CLEARING TROUBLE CODES»(/chevrolet/caprice-impala-ss/1995-1996/remont/testing-diagnostics/#engine-controls-tests-wcodes-43l__clearing-trouble-codes) .
2. 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.
3. 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.
4. If SERVICE ENGINE SOON light does not come on, all stored trouble codes were intermittent failures, except as noted above.

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 conditions under which code will set.

CLEARING TROUBLE CODES

To clear trouble codes from memory, either to determine if malfunction will occur again or after making necessary repairs, disconnect power supply to PCM for at least 30 seconds or clear codes using a scan tester with code clearing capability.

PCM LOCATION

On most models, engine control module is located behind right or left side of dash, behind right or left kick panel or on left or right side of engine compartment. For more precise location, see COMPONENT LOCATIONS in SYSTEM/COMPONENT TESTS - 4.3L article in this section.

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.

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. Most models require the use of a scan tester to enter field service mode. See FIELD SERVICE MODE CHECK in BASIC TESTING article in this section.

Note. Vehicles utilizing a 12-terminal DLC with terminal "B" not used, must use a scan tester for retrieving codes or enter Field Service Mode.

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. On most models scan tester is REQUIRED to retrieve vehicle information. 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 a 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. In addition, special jumper harnesses or testers may be required by manufacturer to facilitate diagnosis.

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 or ON-BOARD DIAGNOSTIC SYSTEM CHECK located in BASIC TESTING article in this section. If vehicle does not pass diagnostic 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.

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, DO NOT use scan tester for diagnosis. Contact tester manufacturer for additional information.

SCAN DATA

Note. Information contained in SCAN DATA 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, more often on most models. 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.

SCAN DATA

ECM/PCM CODE CHARTS

Note. In following diagnostic tests, schematics and illustrations

CODE 11, MALFUNCTION INDICATOR LIGHT

MIL should always be on steady with ignition on and engine stopped. Ignition voltage is supplied directly to bulb. PCM turns on light by providing a path to ground.

Note. Test numbers refer to numbers on diagnostic chart.

1. If MIL driver circuit or ignition feed circuit to bulb is open, MIL will not illuminate.
2. Jumper Harness (J 35616-A) should be used instead of directly probing harness. This will prevent damage to harness.
3. MIL should go off after engine starts. If it does, problem is not present at this time. If light does not go off, drive circuit is shorted to ground or PCM is faulty.
4. If other codes exist, use other code charts first, then restart at beginning of this chart.

If ignition feed circuit is suspected of being open, check and see if other bulbs on that circuit illuminate. Code 11 will cause MIL to remain on, even if malfunction clears.

Code 11 Schematic (Caprice) MIL Circuit. Scheme 4

Code 11 Diagnostic Flow Chart (Caprice) MIL Circuit. Scheme 5

CODE 13, LEFT HEATED OXYGEN SENSOR CIRCUIT OPEN

Note. The 5.7L (VIN P) engine is equipped with 2 oxygen sensors. On this model, code will set if the left sensor circuit is open. Code 63 will set if the right sensor circuit is open. Oxygen sensors use a heating element. Heating element is not controlled by PCM.

Code will set if Codes 21 and 22 are not set, engine is at normal operating temperature, oxygen sensor voltage is constant within a specified range (.35-.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. Most likely causes of code are: open sensor signal (high) circuit, faulty PCM connection, faulty PCM, faulty oxygen sensor connection or faulty oxygen sensor.

Note. Test numbers refer to numbers on diagnostic chart.

1. 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 (steady .35-.55 volt).
2. 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.
3. This tests oxygen sensor circuit wiring. Use only a high impedance (10-megohm minimum) digital voltmeter.

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 3.5-14.0 ohms.

CODE 13 PCM TERMINAL & CIRCUIT WIRING IDENTIFICATION

Code 13 Schematic (Caprice) Open Oxygen Sensor Circuit. Scheme 6

Code 13 Diagnostic Flow Chart (Caprice) Open Oxygen Sensor Circuit. Scheme 7

CODE 14, COOLANT TEMP SENS SGNL VLTGE LOW (HI TEMP INDICATED)

Code will set if PCM sees an extremely high temperature signal (low voltage). Most likely causes of code are: sensor signal circuit shorted to ground, faulty coolant temperature sensor or faulty PCM.

Note. This chart assumes engine cooling system is functioning properly (not overheating). Test numbers refer to numbers on diagnostic chart.

1. This checks if conditions for code still exist.
2. This tests for grounded sensor signal line between control module and coolant sensor.

After engine is started, temperature should rise steadily to about 90°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.

CODE 14 PCM TERMINAL & CIRCUIT WIRING IDENTIFICATION

TEMPERATURE-TO-RESISTANCE VALUES (Measure resistance across sensor terminals)

1. For shared sensor ground tie-offs, see appropriate wiring diagram in WIRING DIAGRAMS section.

Code 14 Schematic (Caprice) Coolant Temperature Sensor Signal Voltage Low (High Temp. Indicated). Scheme 8

Code 14 Diagnostic Flow Chart (Caprice) Coolant Temperature Sensor Signal Voltage Low (High Temp. Indicated). Scheme 9

CODE 15, COOLANT TEMP SENSOR SIGNAL VOLTAGE LOW

Code indicates control module has seen high resistance (high monitored voltage) 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. Most likely causes of code are: open sensor signal circuit, open sensor ground circuit (not allowing path to ground for 5-volt reference), faulty sensor connection, faulty sensor, faulty PCM connection or faulty PCM.

Note. Test numbers refer to numbers on diagnostic chart.

1. This checks if conditions for code still exist.
2. This test simulates a low voltage condition. If control module recognizes low voltage signal, scan tester will display greater than about 130°C. This indicates control module and wiring are not at fault.
3. This test determines if coolant sensor ground or signal circuit is open.

After engine is started, temperature should rise steadily to about 90°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.

CODE 15 PCM TERMINAL & CIRCUIT WIRING IDENTIFICATION

TEMPERATURE-TO-RESISTANCE VALUES (Measure resistance across sensor terminals)

1. For shared sensor ground tie-offs, see appropriate wiring diagram in WIRING DIAGRAMS section.

Code 15 Diagnostic Flow Chart (Caprice) Coolant Temp Sensor Signal Voltage Low. Scheme 10

CODE 16, OPTI-SPARK IGNITION SYSTEM LOW RESOLUTION PULSE

Ignition system supplies 2 timing inputs to PCM, a high resolution signal (360 pulses per camshaft revolution) and a low resolution signal (4 pulses per camshaft revolution). PCM can determine if either timing input is not being received by comparing inputs. If PCM detects high resolution pulse without detecting low pulse, Code 16 will set. Reference signal on resolution line toggles between zero and 5 volts as camshaft turns.

Note. Test numbers refer to numbers on diagnostic chart.

1. If engine starts at this time, code is intermittent.
2. This step determines if PCM is sending out a signal to distributor for processing. If this signal is not available or is shorted to ground or voltage, distributor cannot ground it to produce reference pulses.
3. If Code 41 and/or 42 is also set with Code 16 and no external fault can be found, replace PCM. If only Code 16 is set and distributor connections are okay, replace distributor.

An open, a short to voltage, a short to ground or a defective sensor inside distributor can prevent reference voltage from pulsing at PCM resolution terminal. If Code 16 does not reset and vehicle still does not start, go to NO START - ENGINE CRANKS OKAY in BASIC TESTING article in this section.

Code 16 Schematic (Caprice) Opti-spark Ignition System Low Resolution Pulse. Scheme 11

Code 16 Diagnostic Flow Chart (Caprice) Opti-spark Ignition System Low Resolution Pulse. Scheme 12

CODE 18, INJECTOR CIRCUIT

Injectors are provided voltage when ignition is on. PCM energizes injectors by providing an individual ground for each injector. Injectors are energized on the intake stroke of each cylinder. PCM continuously monitors voltage on each driver circuit. When PCM detects a voltage that is out of range, Code 18 will set.

Note. Test numbers refer to numbers on diagnostic chart.

1. Injector fuses are located in the underhood electrical center.
2. Performing an injector balance test will determine which injector circuit is faulty. See «SYSTEM/COMPONENT TESTS - 4.3L»(/chevrolet/caprice-impala-ss/1995-1996/remont/testing-diagnostics/#engine-controls-systemcomponent-tests-43l) article in this section.
3. See mini-schematic to determine which fuse powers injector banks.
4. When checking injector resistance, injector should be cold.

If an injector is disconnected and then reconnected while engine is running, injector driver is disabled for a predetermined time and Code 18 will set. When driver is disabled, an engine misfire will be evident.

Code 18 Schematic (Caprice) Injector Circuit. Scheme 13

Code 18 Diagnostic Flow Chart (Caprice) Injector Circuit. Scheme 14

CODE 21, THROTTLE POSITION SENSOR SIGNAL VOLTAGE HIGH

Code will set if engine is idling (closed throttle), MAP value is low, a MAP code is not set and PCM sees high TP sensor voltage. Most likely causes for code are: TP sensor signal circuit shorted to voltage, open sensor ground circuit, faulty sensor connection, faulty TP sensor or faulty PCM.

Note. Test numbers refer to numbers on diagnostic chart.

1. This test checks if code is result of a hard failure or an intermittent condition.
2. This test simulates a low-voltage condition. If control module recognizes change of state, control module and wiring are okay.
3. 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.

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.

CODE 21 PCM TERMINAL & CIRCUIT WIRING IDENTIFICATION

1. For shared sensor ground tie-offs, see appropriate wiring diagram in WIRING DIAGRAMS section.

Code 21 Schematic (Caprice) Throttle Position Sensor Signal Voltage High. Scheme 15

Code 21 Diagnostic Flow Chart (Caprice) Throttle Position Sensor Signal Voltage High. Scheme 16

CODE 22, THROTTLE POSITION SENSOR SIGNAL VOLTAGE LOW

Code will set if engine is running and TP sensor voltage is lower than base idle voltage (auto zero voltage). Most likely causes of code are: TP sensor signal circuit open or shorted to ground, 5-volt reference open or shorted to ground (should also set other codes), faulty sensor connection, faulty sensor, faulty PCM connection or faulty PCM.

Note. Test numbers refer to numbers on diagnostic chart.

1. This test checks if code is result of a hard failure or an intermittent condition.
2. This test simulates high voltage conditions. If control module recognizes change of state, control module and wiring are okay.
3. This simulates a high signal voltage to check for an open in TP sensor signal line to control module. Scan tester should recognize this signal and display high TP sensor voltage.

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.

CODE 22 PCM TERMINAL & CIRCUIT WIRING IDENTIFICATION

1. For shared sensor ground tie-offs, see appropriate wiring diagram in WIRING DIAGRAMS section.

Code 22 Diagnostic Flow Chart (Caprice) Throttle Position Sensor Signal Voltage Low. Scheme 17

CODE 23, IAT SENSOR SIGNAL VOLTAGE HIGH (LOW TEMP INDICATED)

Code will set if engine has been running for a precalibrated period of time, has reached operating temperature and signal voltage indicates a low intake air temperature (high voltage). Most likely causes of code are: open sensor signal circuit, open sensor ground circuit (not allowing path to ground for 5-volt reference), faulty sensor connection, faulty sensor, faulty PCM connection or faulty PCM.

Note. Test numbers refer to numbers on diagnostic chart.

1. Checks if code is result of a hard failure or an intermittent condition.
2. This simulates low voltage (high temperature) conditions. If scan tester displays a high temperature, control module and wiring are not at fault.
3. This checks for continuity of sensor signal and ground circuits using process of elimination. If ground circuit is shared by other sensors and ground circuit is open, accompanying codes related to those sensors may be present.

If engine is allowed to cool overnight, coolant and IAT 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.

CODE 23 PCM TERMINAL & CIRCUIT WIRING IDENTIFICATION

TEMPERATURE-TO-RESISTANCE VALUES (Measure resistance across sensor terminals)

1. For shared sensor ground tie-offs, see appropriate wiring diagram in WIRING DIAGRAMS section.

Code 23 Schematic (Caprice) IAT Sensor Signal Voltage High (Low Temp Indicated). Scheme 18

Code 23 Diagnostic Flow Chart (Caprice) IAT Sensor Signal Voltage High (Low Temp Indicated). Scheme 19

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 about 2 MPH. Voltage level and pulses increase with vehicle speed. Control module converts pulsing voltage to MPH, which is used by control module to calculate vehicle adjustments.

Note. Test numbers refer to numbers on diagnostic chart.

Note. Prior to testing Corvette for Code 24, disable ASR system.

1. PM generator only produces a voltage signal if drive wheels are turning greater than about 2 MPH.

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.

Code 24 Schematic (Caprice) Vehicle Speed Sensor. Scheme 20

Code 24 Diagnostic Flow Chart (Caprice) Vehicle Speed Sensor. Scheme 21

CODE 25, IAT SENSOR SIGNAL VOLTAGE LOW (HIGH TEMP INDICATED)

Code will set if intake air temperature is extremely high (sensor signal voltage low) for a precalibrated period of time. Most likely causes of code are: sensor signal circuit shorted to ground, faulty coolant temperature sensor or faulty PCM.

Note. Test numbers refer to numbers on diagnostic chart.

1. This checks if code is hard failure or intermittent condition.
2. This simulates low temperature (high resistance) conditions. If control module recognizes open circuit and scan tester displays temperature of less than about -30°C, control module and wiring are okay.

If engine is allowed to cool overnight, coolant temperature sensor and IAT 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.

CODE 25 PCM TERMINAL & CIRCUIT WIRING IDENTIFICATION

TEMPERATURE-TO-RESISTANCE VALUES (Measure resistance across sensor terminals)

1. For shared sensor ground tie-offs, see appropriate wiring diagram in WIRING DIAGRAMS section.

Code 25 Diagnostic Flow Chart (Caprice) IAT Sensor Signal Voltage Low (High Temp Indicated). Scheme 22

CODE 26, CANISTER PURGE SOLENOID

Solenoid is supplied voltage when ignition is on. PCM controls solenoid valve by providing a ground through one of its Quad-Drivers Modules (QDM). When solenoid is actuated, terminal is grounded and its monitored voltage will be low. When an output is off, its terminal voltage will be high. Each QDM has a separate fault line to indicate presence of a current fault to control module central processor.

Note. Test numbers refer to numbers on diagnostic chart.

1. Code 26 will set if the PCM detects the wrong voltage potential. Test will determine if solenoid can be controlled by PCM.
2. 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.
3. The remaining checks will identify a circuit problem that has caused an excessive current flow or inoperative solenoid.

Check related harness connectors, including PCM harness. Check for damaged or pushed out terminals.

Code 26 Schematic (Caprice) Canister Purge Solenoid. Scheme 23

Code 26 Diagnostic Flow Chart (Caprice) Canister Purge Solenoid. Scheme 24

CODE 27, EGR SOL VALVE

Ignition voltage is supplied voltage when ignition is on. PCM controls solenoid valve by providing a ground through one of its Quad-Drivers Modules (QDM). When solenoid is actuated, terminal is grounded and its monitored voltage will be low. When an output is off, its terminal voltage will be high. Each QDM has a separate fault line to indicate presence of a current fault to control module central processor.

Note. Test numbers refer to numbers on diagnostic chart.

1. Code 27 will set if the PCM detects the wrong voltage potential. Test will determine if solenoid can be controlled by PCM.
2. 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.
3. The remaining checks will identify a circuit problem that has caused an excessive current flow or inoperative solenoid.

Check related harness connectors, including PCM harness. Check for damaged or pushed out terminals.

Code 27 Schematic (Caprice) EGR Solenoid Valve. Scheme 25

Code 27 Diagnostic Flow Chart (Caprice) EGR Solenoid Valve. Scheme 26

CODE 28, TRANS. RANGE PRESSURE SWITCH

Transmission range pressure switch assembly consists of 5 pressure switches (2 normally closed, 3 normally open), and a fluid temperature sensor combined into one unit and mounted on the valve body. PCM supplies voltage to each range signal. By grounding one or more of these circuits through various combinations of pressure switches, PCM detects which manual valve position has been selected. With ignition on and engine off, Park/Neutral will be indicated. Code 28 will set when range signals "A" and "C" are both zero volts (on) for 2 seconds.

Note. Test numbers refer to numbers on diagnostic chart.

1. Checks indicated range signal to valve position signal actually selected.
2. Checks for correct voltage from PCM to transmission external connector.
3. Checks for short to ground in any one of the 3 valve position circuits.

Code will set if PCM detects one of 2 illegal combinations. Check all connections for good contact.

Code 28 Schematic (Caprice) Transmission Range Pressure Switch. Scheme 27

Code 28 Diagnostic Flow Chart (Caprice) Transmission Range Pressure Switch. Scheme 28

CODE 29, SECONDARY AIR INJECTION

Ignition voltage is supplied voltage when ignition is on. PCM controls air pump relay by providing a ground through one of its Quad-Driver Modules (QDM). When relay is actuated, terminal is grounded and its monitored voltage will be low. When an output is off, its terminal voltage will be high. Each QDM has a separate fault line to indicate presence of a current fault to control module central processor.

Note. Test numbers refer to numbers on diagnostic chart.

1. Code 29 will set if the PCM detects the wrong voltage potential. Test will determine if relay can be controlled by PCM.
2. 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.
3. The remaining checks will identify a circuit problem that has caused an excessive current flow or inoperative relay.

Check related harness connectors, including PCM harness. Check for damaged or pushed out terminals.

Code 29 Schematic (Caprice) Secondary Air Injection. Scheme 29

CODE 32, EGR SYSTEM ERROR

EGR vacuum is regulated by an PCM-controlled, normally closed solenoid. PCM will turn EGR on and off (duty cycle) by grounding and ungrounding solenoid drive circuit. Duty cycle is calculated by PCM based on coolant temperature, airflow and engine RPM. PCM will check EGR operation when vehicle speed is 16-32 MPH, MAP is within calibrated range, throttle angle is zero percent and vehicle is coasting.

Note. Test numbers refer to numbers on diagnostic chart.

1. See following: Plugged Intake Passage 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. 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.
2. Using Tech 1 tester, EGR solenoid should energize and allow vacuum to be applied to gauge. Vacuum at gauge may or may not slowly bleed off; however, gauge is able to read amount of vacuum being applied.
3. Upon exiting field service mode, gauge vacuum should bleed off through a vent in solenoid. Pump gauge vacuum may or may not bleed off; this does not indicate a problem.
4. Remaining tests check ability of EGR valve to interact with exhaust system. This system uses a negative backpressure EGR valve which will hold vacuum with engine off.
5. 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.

Code 32 Schematic (Caprice) EGR System Error. Scheme 30

Code 32 Diagnostic Flow Chart - 1 Of 2 (Caprice) EGR System Error. Scheme 31

Code 32 Diagnostic Flow Chart - 2 Of 2 (Caprice) EGR System Error. Scheme 32

CODE 33, MAP SENSOR SIGNAL VOLTAGE HIGH

Code 33 will set when MAP signal voltage reading is high for greater than a precalibrated period of time, TPS voltage indicates throttle is closed and neither Code 21 nor 22 is present. Most likely causes for code are: open sensor ground circuit, sensor signal circuit shorted to voltage, faulty MAP sensor, MAP sensor vacuum leak or faulty PCM.

Note. Test numbers refer to numbers on diagnostic chart.

1. This test confirms Code 33 and determines if it is result of a hard failure or an intermittent condition.
2. 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.

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.

CODE 33 PCM TERMINAL & CIRCUIT WIRING IDENTIFICATION

1. For shared sensor reference and shared sensor ground tie-offs, see appropriate wiring diagram in WIRING DIAGRAMS section.

Code 33 Schematic (Caprice) MAP Sensor Signal Voltage High. Scheme 33

Code 33 Diagnostic Flow Chart (Caprice) MAP Sensor Signal Voltage High. Scheme 34

CODE 34, MAP SENSOR SIGNAL VOLTAGE LOW

Code 34 will set when ignition is on, throttle is off idle, no TP sensor code exists and MAP signal voltage is lower than expected for off idle engine operation. Most likely causes for code are: MAP sensor signal circuit open or shorted to ground, 5-volt reference circuit open or shorted to ground, faulty sensor connection, faulty sensor or faulty PCM.

Note. Test numbers refer to numbers on diagnostic chart.

1. This confirms conditions for Code 34 and determines if code was caused by a hard failure or an intermittent fault.
2. 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.
3. 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.

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.

CODE 34 PCM TERMINAL & CIRCUIT WIRING IDENTIFICATION

1. For shared sensor reference and shared sensor ground tie-offs, see appropriate wiring diagram in WIRING DIAGRAMS section.

Code 34 Diagnostic Flow Chart (Caprice) MAP Sensor Signal Voltage Low. Scheme 35

CODE 36, OPTI-SPARK HIGH RESOLUTION PULSE

Ignition system supplies 2 timing inputs to PCM, a high resolution signal (360 pulses per camshaft revolution) and a low resolution signal (8 pulses per camshaft revolution). PCM can determine if either timing input is not being received by comparing inputs. If PCM detects 40 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.

1. Determines if code is intermittent.
2. This step determines if PCM is sending out a signal to distributor for processing. If this signal is not available or is shorted to ground or voltage, distributor cannot ground it to produce reference pulses.
3. If Code 41 and/or 42 is set with Code 36 and no external fault can be found, replace PCM. If Code 36 is set alone and distributor connections are okay, replace distributor.

An open, a short to voltage, a short to ground or a defective sensor inside distributor can prevent reference voltage from pulsing at PCM resolution terminal. If Code 36 is present and vehicle still does not start, check for Code 16 and use that chart first. If vehicle still will not start, go to NO START - ENGINE CRANKS OKAY in BASIC TESTING article in this section.

Code 36 Diagnostic Flow Chart (Caprice) Opti-Spark High Resolution Pulse. Scheme 36

CODE 37, TCC BRAKE SWITCH ERROR

PCM monitors activity of the normally-closed brake switch. Switch opens when brake pedal is applied.

Note. Test numbers refer to numbers on diagnostic chart.

1. Checks for voltage at brake switch.
2. Simulates brake switch closed or brakes off.
3. Checks TCC brake switch circuit between PCM and switch.

Code 37 can be caused by a misadjusted brake switch or a poor connection. Code may also be set by unusual driving habits (i.e. stop-and-go expressway driving).

Code 37 Schematic (Caprice) TCC Brake Switch Error. Scheme 37

Code 37 Diagnostic Flow Chart (Caprice) TCC Brake Switch Error. Scheme 38

CODE 38, BRAKE SWITCH ERROR

PCM monitors activity of the normally-closed brake switch. Switch opens when brake pedal is applied. Code will set if PCM has seen conditions which would have required brake applications at least 7 times and no transition in brake switch has been detected.

Note. Test numbers refer to numbers on diagnostic chart.

1. Checks for voltage at brake switch.
2. Simulates brake switch closed or brakes off. Checks brake switch circuit between PCM and switch.
3. Checks circuit between brake switch and PCM.

Code may also be set by unusual driving habits (i.e. stop-and-go expressway driving).

Code 38 Diagnostic Flow Chart (Caprice) Brake Switch Error. Scheme 39

CODE 41, OPTI-SPARK IGNITION SYSTEM OPEN OR SHORTED EST CKT

Ignition system provides 2 timing inputs to PCM, high resolution (360 pulses per camshaft revolution) and low resolution (4 pulses per crankshaft revolution). PCM uses these 2 inputs to determine individual spark timing for each cylinder. Once PCM calculates ignition timing, timing signal will be sent to ignition coil driver on IC circuit. Each timing pulse received by ignition coil driver will trigger coil driver to operate ignition coil. IC signal voltage ranges from about .5 volt to 4.5 volts. If a Code 41 is set, PCM will disable fuel injectors to prevent flooding of engine.

Note. Test numbers refer to numbers on diagnostic chart.

1. Determines if code is intermittent.
2. This step determines if IC signal from PCM is available at ignition coil driver. IC circuit voltage should be between about .5 volt and 4.5 volts.
3. Remaining steps ensure coil driver circuitry is okay. If all wiring and connections are okay, check ignition coil and ignition coil voltage supply.

Because coil driver gets its power from coil, check ignition feed circuit to ignition coil for opens, including coil fuse.

Code 41 Diagnostic Flow Chart (Caprice) Opti-Spark Ignition System Open Or Shorted EST Circuit. Scheme 40

CODE 42, IC CIRCUIT GROUNDED

Ignition system provides 2 timing inputs to PCM, high resolution (360 pulses per camshaft revolution) and low resolution (4 pulses per crankshaft revolution). PCM uses these 2 inputs to determine individual spark timing for each cylinder. Once PCM calculates ignition timing, timing signal will be sent to ignition coil driver on IC circuit. Each timing pulse received by ignition coil driver will trigger coil driver to operate ignition coil. IC signal voltage ranges from about .5 volt to 4.5 volts.

Note. Test numbers refer to numbers on diagnostic chart.

1. If engine starts, code is intermittent.
2. This test checks for an IC signal from PCM to ignition coil driver.
3. Remaining tests check driver circuitry. Because coil driver gets its power from coil, check ignition coil feed circuit to ignition coil for opens.

Code 42 Diagnostic Flow Chart (Caprice) IC Circuit Grounded. Scheme 41

CODE 43, KNOCK SENSOR CIRCUIT (DUAL SENSORS)

Knock sensor informs PCM of engine detonation. PCM will retard ignition timing based on signals from knock sensors. Knock sensors produce an AC voltage signal which is proportional to amount of engine detonation (knock). Internal sensor circuitry causes 5-volt DC reference signal sent by PCM to be pulled low to about 1.5 volts. Any AC voltage produced by sensors will travel to PCM on this same reference line. Code 43 will set if: one sensor circuit becomes open, resulting in a 2.2 to 4.1-volt reference being monitored by PCM, both sensor circuits become open, resulting in a reference voltage greater than 4.1 volts being seen by PCM, or one or both circuits become grounded, resulting in a low (less than .78 volt) reference voltage being seen by PCM.

If an audible knock is heard from engine, repair internal engine problem, as normally no knock should be detected at idle. PCM supplies 5 volts on knock sensor circuit which should be present at knock sensor terminals when sensors are disconnected. If knock sensor circuit is shorted to voltage, Code 43 will set. With both sensors and PCM disconnected, no voltage should be present. An improperly installed sensor can prevent knock sensor from grounding to block.

Note. Test numbers refer to numbers on diagnostic chart.

1. If an audible knock is heard from engine, repair internal engine problem, as normally no knock should be detected at idle.
2. Determines if knock sensor is faulty or if module is faulty.
3. Sensor signal circuit shorted to voltage will set code. With sensor and PCM unplugged, no voltage should be present.
4. An improperly installed sensor can cause code to set.
5. If short to battery voltage is found, additional component damage may have occurred. If code resets after repairs, rerun chart to detect additional faults.

PCM has the ability to diagnose opens and shorts on knock sensor circuit. Scan tester will display if one or both sensors are open, or if both are grounded. Also, ensure knock sensor module is properly installed.

Code 43 Schematic (Caprice) Knock Sensor Circuit (Dual Sensors). Scheme 42

Code 43 Diagnostic Flow Chart (Caprice) Knock Sensor Circuit (Dual Sensors). Scheme 43

CODE 44, LEFT HEATED OXYGEN SENSOR LEAN EXHAUST INDICATION

Note. Models 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.

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 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.

Code is set when O2 sensor voltage signal at control module is low (less than 0.3 volt) for a precalibrated period and fuel system is operating in "closed loop" and attempting to richen mixture. Most likely causes for setting of code are: an actual lean condition, a short to ground on sensor signal circuit or a faulty PCM.

Note. Test number refers to number on diagnostic chart.

1. Checks to see if O2 sensor is registering a lean condition.

Using scan tester, observe Block Learn Memory (BLM) value at different RPMs. If conditions for a lean exhaust code 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, setting code.

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.

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, code may set. If code is intermittent, see INTERMITTENTS in TESTS W/O CODES article in this section.

CODE 44 PCM TERMINAL & CIRCUIT WIRING IDENTIFICATION

Code 44 Diagnostic Flow Chart (Caprice) Lean Exhaust Indication. Scheme 44

CODE 45, LEFT HEATED OXYGEN SENSOR RICH EXHAUST INDICATION

Note. Models 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.

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, ignition shielding (ground), vapor canister fuel saturation, coolant sensor, MAP sensor, O2 sensor contamination and TPS intermittent output.

Code is set when fuel system is operating in "closed loop", throttle angle is greater than idle, O2 sensor signal at control module is greater than .7 volt for a precalibrated period, fuel system is attempting to lean mixture and time since engine start is one minute or more. Most likely causes of code are: an actual rich condition, a short to voltage on sensor signal circuit or a faulty PCM.

Note. Test number refers to number on diagnostic chart.

1. Test checks to see if O2 sensor is registering a rich condition.

If other codes of lower number are set with code, use those charts first. Malfunction in MAP or TPS sensor circuits can cause a rich exhaust code to set. If other codes are not set, rich exhaust is most likely caused by

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 will be set if air/fuel ratio becomes too rich.

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.

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.

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.

TPS

An intermittent TPS output will cause system to operate rich due to a false indication of engine acceleration.

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.

EGR Problem

EGR valve sticking open at idle is usually accompanied by a rough idle and/or stalling. Also check for shorted/leaking injector and fuel-contaminated oil. If code is intermittent, see INTERMITTENTS in TESTS W/O CODES article in this section.

CODE 45 PCM TERMINAL & CIRCUIT WIRING IDENTIFICATION

Code 45 Diagnostic Flow Chart (Caprice) Rich Exhaust Indication. Scheme 45

CODE 46, PASS-KEY CIRCUIT

The PASS-Key system is designated to disable vehicle operation if the incorrect key or starting procedure is used. PASS-Key decoder module sends a signal to the PCM if the correct key is being used. If the proper signal does not reach the PCM, the PCM will not pulse the injectors, thus not allowing the vehicle to start. Code 46 will set if proper signal is not being received on fuel enable signal circuit to PCM when ignition is turned on.

Note. Test numbers refer to numbers on diagnostic chart.

1. If engine cranks but does not start, it indicates the portion of the module which generates the signal to the PCM is not operating or fuel enable signal circuit is open, shorted to ground or possibly shorted to voltage. If decoder module is found to be okay, PCM may be at faulty, but this not a likely condition.
2. If Code 46 is stored and engine will not crank, it indicates that there is a Pass-Key problem or incorrect key or starting procedure is being used.

Pass-Key Diagnosis

Note. For complete system diagnosis, see ANTI-THEFT SYSTEM article in the ACCESSORIES/SAFETY EQUIPMENT section.

PASS-Key is a sophisticated system that interfaces PCM and starter with a power source, decoder module, starter enable relay, ignition switch and instrument cluster. Check system for following common problems

1. Ensure ignition key resistor pellet is not cracked, dirty or coated. Ensure excess plastic does not exist around pellet contacts.
2. Check ignition key pellet sensing contacts in ignition lock cylinder. Look into cylinder lock. If contacts are damaged or are not Silver in color, replace cylinder lock.
3. Check related fuses.
4. Check security indicator bulb in the instrument panel.

A defective resistor pellet within ignition key or incorrect resistance value of key (15 different assigned values) will prevent vehicle from starting. Key must be correct electrically and mechanically. If incorrect key is used to try to start vehicle, decoder will not allow vehicle to start for 2-4 minutes, even after correct key is inserted.

If starter enable relay must be replaced, check circuit to starter solenoid for possible short. A short may have caused relay to fail.

Code 46 Schematic (Caprice) Pass-Key Circuit. Scheme 46

CODE 47, KNOCK SENSOR MODULE

Knock sensor module is located inside PCM.

Code 47 Diagnostic Flow Chart (Caprice) Knock Sensor Module. Scheme 47

CODE 48, MASS AIRFLOW SENSOR

Mass airflow meter measures amount of induction airflow. This information is used by PCM to determine adjustments to air/fuel ratio. MAF sensor is a hot-wire type. Sensor maintains hot wire at a predetermined temperature. The greater the airflow across the hot wire, the more current is required to maintain hot wire temperature. Sensor changes the current requirements into a frequency signal which is read by the PCM. The PCM calculates airflow based upon this signal.

Note. Test numbers refer to numbers on diagnostic charts.

1. Determines if fault is a hard failure or an intermittent condition.
2. Checks for 5-volt reference from PCM.
3. Verifies both ignition voltage and a good ground circuit are available.

An intermittent may be caused by a poor connection, mis-routed harness, rubbed through wire insulation or a broken wire inside insulation. Code 48 could be caused by a vacuum leak. Check short and long term fuel trim for being in optimum range (both banks).

Code 48 Schematic (Caprice) Mass Airflow Sensor. Scheme 48

Code 48 Diagnostic Flow Chart (Caprice). Scheme 49

CODE 50, SYSTEM VOLTAGE LOW

PCM monitors voltage on ignition feed circuit (Pink wire). Normal voltage is 9.6-16 volts. If voltage drops below 8 volts, Code 50 will set and Malfunction Indicator Light (MIL) will illuminate.

An open in ignition feed circuit (Pink wire) or extremely low voltage may cause loss of serial data, no start condition and malfunction of the MIL. Additional codes may be set.

Code 50 Schematic (Caprice) System Voltage Low. Scheme 50

Code 50 Schematic (Caprice) System Voltage Low. Scheme 51

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.

CODE 53, SYSTEM VOLTAGE HIGH

This code indicates a basic charging system problem. Code 53 will set when voltage at control module terminal is greater than specification for a precalibrated time. If voltage at PCM battery voltage terminal is not within specification, check and repair charging system.

CHARGING SYSTEM SPECIFICATIONS

Code 53 Schematic (Caprice) System Voltage High. Scheme 52

Code 53 Diagnostic Flow Chart (Caprice) System Voltage High. Scheme 53

CODE 55, PCM ERROR

Ensure PCM grounds are okay. Ensure correct EPROM is being used and that it is properly installed. If okay, replace PCM. Clear codes, confirm closed loop operation and check operation of Malfunction Indicator Light (MIL).

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.

Low fuel pressure or restricted fuel flow may cause a lean condition. Check for plugged injectors, poor or contaminated fuel, low fuel level and restricted fuel supply. Vapor lock can also cause Code 55.

Code 55 Schematic (Caprice) Fuel Lean Monitor. Scheme 54

CODE 58, TRANS TEMPERATURE SENSOR HIGH TEMPERATURE

Temperature sensor is a 2 wire thermistor located in transaxle. This sensor operates in the same manner as engine coolant temperature sensor and intake air temperature sensor. PCM applies 5 volts to sensor on signal circuit. Voltage sensed at PCM signal circuit terminal will be high when transmission fluid is cold and as fluid warms voltage signal will drop. A very low signal voltage indicates a high fluid temperature or a failure in sensor circuit. Normal fluid temperature range is 75-100°C.

Code 58 will set when sensor indicates a high fluid temperature for a precalibrated period of time. Malfunction Indicator Light (MIL) will illuminate and PCM will use a warm default sensor value.

Note. Test numbers refer to numbers on diagnostic chart.

1. Checks for a short to ground or an out-of-calibration sensor.
2. Checks for an internal fault within the transmission by creating an open.

Check harness routing for a potential short to ground in signal circuit. Temperature should rise steadily to about 90°C then stabilize. A skewed sensor could result in delayed shifts or TCC enabled complaints.

Use temperature-to-resistance table to check sensor at various levels to determine if sensor is out-of-calibration, which could result in firm shifts or TCC enable.

TEMPERATURE-TO-RESISTANCE VALUES (1)

Code 58 Diagnostic Flow Chart (Caprice) Transmission Temperature Sensor High Temperature. Scheme 55

CODE 59, TRANS. TEMPERATURE SENSOR LOW TEMPERATURE

Temperature sensor is a 2 wire thermistor located in transaxle. This sensor operates in the same manner as engine coolant temperature sensor and intake air temperature sensor. PCM applies 5 volts to sensor on signal circuit. Voltage sensed at PCM signal circuit terminal will be high when transmission fluid is cold and as fluid warms voltage signal will drop. A very high signal voltage indicates a low fluid temperature or a failure in sensor circuit. Normal fluid temperature range is 75-100°C.

Code 59 will set when sensor indicates a low temperature for a precalibrated period of time. Malfunction Indicator Light (MIL) will not illuminate and PCM will use a warm default sensor value.

Note. Test numbers refer to numbers on diagnostic chart.

1. This test determines if a current condition exists.
2. Simulates a Code 58. If PCM recognizes low signal voltage, and scan displays about 146°C or higher, PCM and wiring are okay.
3. Checks if signal circuit is open. Five volts should be present at sensor connector.

Temperature should rise steadily to about 90°C, then stabilize. A faulty connection or an open in ground or signal circuit can result in Code 59. A skewed sensor could result in firm shifts or TCC enabled complaints. Use temperature-to-resistance table to check sensor at various levels to determine if sensor is out-of-calibration, which could result in firm shifts or TCC enable.

TEMPERATURE-TO-RESISTANCE VALUES (1)

Code 59 Diagnostic Flow Chart (Caprice) Transmission Temperature Sensor Low Temperature. Scheme 56

CODE 63, RIGHT HEATED OXYGEN SENSOR CIRCUIT OPEN

Note. Engine is equipped with 2 oxygen sensors. On this model, code will set if the right sensor circuit is open. Code 13 will set if the left sensor circuit is open. Oxygen sensors use a heating element. Heating element is not controlled by PCM.

Code will set if Codes 21 and 22 are not set, engine is at normal operating temperature, oxygen sensor voltage is constant within a specified range (.35-.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. Most likely causes of code are: open sensor signal (high) circuit, faulty PCM connection, faulty PCM, faulty oxygen sensor connection or faulty oxygen sensor.

Note. Test numbers refer to numbers on diagnostic chart.

1. 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 (steady .35-.55 volt).
2. 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.
3. This tests oxygen sensor circuit wiring. Use only a high impedance (10-megohm minimum) digital voltmeter.

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 63 being set. On models equipped with an oxygen sensor heating element, element resistance should be 3.5-14.0 ohms.

CODE 63 PCM TERMINAL & CIRCUIT WIRING IDENTIFICATION

CODE 64, RIGHT HEATED OXYGEN SENSOR LEAN EXHAUST INDICATION

Note. Models are equipped with 2 oxygen sensors. On these models, Code 64 will set if the right sensor circuit is lean. Code 44 will set if the left sensor circuit is lean.

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.

Code is set when O2 sensor voltage signal at control module is low (less than 0.3 volt) for a precalibrated period and fuel system is operating in "closed loop" and attempting to richen mixture. Most likely causes for setting of code are: an actual lean condition, a short to ground on sensor signal circuit or a faulty PCM.

Note. Test number refers to number on diagnostic chart.

1. Checks to see if O2 sensor is registering a lean condition.

Using scan tester, observe Block Learn Memory (BLM) value at different RPMs. If conditions for a lean exhaust code exist, block learn value will be about 150.

O2 sensor wire may be mispositioned and laying against exhaust manifold. Check for ground between sensor and wire connector.

Water, even small amounts, near in-tank fuel pump inlet can be delivered to injector. Water may cause a lean exhaust, setting code.

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.

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.

If engine misfires or stalls (including running out of fuel) while vehicle is moving, code may set. If code is intermittent, see INTERMITTENTS in TESTS W/O CODES article in this section.

CODE 64 PCM TERMINAL & CIRCUIT WIRING IDENTIFICATION

CODE 65, RIGHT HEATED OXYGEN SENSOR RICH EXHAUST INDICATION

Note. Models are equipped with 2 oxygen sensors. On these models, Code 65 will set if the right sensor circuit is rich. Code 45 will set if the left sensor circuit is lean.

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, ignition shielding (ground), vapor canister fuel saturation, coolant sensor, MAP sensor, O2 sensor contamination and TPS intermittent output.

Code is set when fuel system is operating in "closed loop", throttle angle is greater than idle, O2 sensor signal at control module is greater than .7 volt for a precalibrated period, fuel system is attempting to lean mixture and time since engine start is one minute or more. Most likely causes of code are: an actual rich condition, a short to voltage on sensor signal circuit or a faulty PCM.

Note. Test number refers to number on diagnostic chart.

1. Test checks to see if O2 sensor is registering a rich condition.

If other codes of lower number are set with code, use those charts first. Malfunction in MAP or TPS sensor circuits can cause a rich exhaust code to set. If other codes are not set, rich exhaust is most likely caused by

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 will be set if air/fuel ratio becomes too rich.

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.

Fuel saturation of charcoal canister will cause a rich air/fuel ratio. If canister is full of fuel, check canister control valves and hoses.

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.

An intermittent TPS output will cause system to operate rich due to a false indication of engine acceleration.

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.

EGR valve sticking open at idle is usually accompanied by a rough idle and/or stalling. Also check for shorted/leaking injector and fuel-contaminated oil. If code is intermittent, see INTERMITTENTS in TESTS W/O CODES article in this section.

CODE 65 PCM TERMINAL & CIRCUIT WIRING IDENTIFICATION

CODE 66, A/C PRESSURE SENSOR

A/C pressure sensor responds to changes in A/C refrigerant system high side pressure. PCM uses A/C compressor load input to determine engine idle speed. Sensor uses a 5-volt reference signal from PCM and returns an input signal to PCM on a separate line. Low pressure (zero psi) will return a signal of about .1 volt. High pressure will return a signal of about 4.6 volts.

Note. Test numbers refer to numbers on diagnostic chart.

1. Checks voltage signal from A/C pressure sensor to PCM. Normal voltage is 0.1-1.8 volts.
2. 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.
3. 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.
4. 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.

Code 66 sets when signal voltage falls outside normal sensor range and is not due to a A/C system problem. If problem is intermittent, check for opens or shorts in harness and poor connections. If wiring is okay, replace pressure sensor. If code resets, replace PCM.

Code 66 Schematic (Caprice) A/C Pressure Sensor. Scheme 57

Code 66 Diagnostic Flow Chart (Caprice) A/C Pressure Sensor. Scheme 58

CODE 67, A/C PRESSURE SENSOR

PCM determines when A/C clutch is engaged by monitoring A/C status line. If A/C pressure does not increase by at least 4 psi when A/C clutch is turned on, Code 67 will set.

Note. Test numbers refer to numbers on diagnostic chart.

1. Code 67 will set if PCM does not detect an A/C pressure change when A/C clutch has been cycled.
2. If relay power feed is intermittent, A/C clutch status terminal may not detect voltage when A/C is commanded on.
3. Check A/C electrical harness for problems. If A/C clutch status line becomes intermittently open or shorted while compressor is on, PCM will be wrongly detecting A/C clutch going on and off. When this occurs and clutch remains engaged, PCM will not detect pressure change and a Code 67 will be set.
4. If A/C compressor clutch status circuit is intermittently open or shorted while compressor is on, PCM will wrongly detect compressor cycling on and off, but PCM will detect no pressure change and a Code 67 will set.

A Code 67 will store in PCM memory but will not turn on the SERVICE ENGINE SOON light. An A/C system low on charge could cause a Code 67 to set.

Code 67 Diagnostic Flow Chart (Caprice) A/C Pressure Sensor. Scheme 59

CODE 68, A/C RELAY CIRCUIT SHORTED

When PCM detects A/C has been requested, PCM will activate A/C clutch relay. When relay is activated, voltage should be present at both A/C compressor clutch and A/C clutch status terminal at PCM. If PCM detects voltage on A/C status line when A/C has not been commanded on, Code 68 will set. A short to voltage anywhere on A/C status line, or stuck relay contacts, will set Code 68. When Code 68 is set, PCM does not turn on SERVICE ENGINE SOON light.

Note. Test numbers refer to numbers on diagnostic chart.

1. A/C must be off while performing test.
2. This step will isolate ignition feed portion of circuit from clutch circuit.
3. If Code 68 reappears at this step, PCM is internally shorted to voltage.

Check for intermittent shorts to A/C clutch circuit or sticking A/C relay.

Code 68 Diagnostic Flow Chart (Caprice) A/C Relay Circuit Shorted. Scheme 60

CODE 69, A/C COMPRESSOR RELAY

When PCM detects A/C has been requested, PCM will activate the A/C clutch relay. When the relay has been activated, voltage should be present at both the A/C compressor clutch and the A/C clutch status line terminal of the PCM. If the PCM activates the A/C clutch relay but does not detect voltage present at A/C status terminal for more than 10 seconds, Code 69 will set. An open or short to ground at any point in the A/C status circuit will cause Code 69 to set. A Code 69 fault will be stored in PCM memory but will not turn on the SERVICE ENGINE SOON light.

Note. Test numbers refer to numbers on diagnostic chart.

1. A problem that may prevent compressor from engaging may or may not cause Code 69 to set.
2. If the A/C compressor clutch operates properly and scan tester indicates A/C status off, then an open exists between the PCM and the splice to the compressor.

Code 69 Diagnostic Flow Chart (Caprice) A/C Compressor Relay. Scheme 61

CODE 70, A/C COMPRESSOR RELAY DRIVER

Relay is supplied voltage when ignition is on. PCM controls solenoid valve by providing a ground through one of its Quad-Driver Modules (QDM). When relay is actuated, terminal is grounded and its monitored voltage will be low. When an output is off, its terminal voltage will be high. Each QDM has a separate fault line to indicate presence of a current fault to control module central processor.

Note. Test numbers refer to numbers on diagnostic chart.

1. Tech 1 will enable circuit for 5 seconds.
2. 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.
3. The remaining checks will identify a circuit problem that has caused an excessive current flow or inoperative relay.

Check related harness connectors, including PCM harness. Check for damaged or pushed out terminals.

Code 70 Diagnostic Flow Chart (Caprice) A/C Compressor Relay Driver. Scheme 62

CODE 72, VEHICLE SPEED SENSOR LOSS

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 about 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.

1. An intermittent connection at VSS or PCM may cause code to set. Inspect harness and all related connections. Check for damage or pushed out terminals.
2. Ensure harness is routed away from hot exhaust components.
3. If software/calibration is incorrect, code will set. Ensure calibration is correct before replacing PCM.

Code 72 Diagnostic Flow Chart (Caprice) Vehicle Speed Sensor Loss. Scheme 63

CODE 73, PRESSURE CONTROL SOLENOID

Pressure control solenoid is a PCM-controlled device used to regulate transmission line pressure. PCM compares TPS voltage, engine RPM and other inputs to determine proper line pressure for a given load. PCM regulates pressure by applying a varying amperage to pressure control solenoid. Amperage varies from 0.1 to 1.1 amps.

Note. Test numbers refer to numbers on diagnostic chart.

1. Checks ability of the PCM to command pressure control solenoid.
2. Checks for voltage at PCM.

Check for poor connections at PCM and at transmission connector.

Code 73 Schematic (Caprice) Pressure Control Solenoid. Scheme 64

Code 73 Diagnostic Flow Chart (Caprice) Pressure Control Solenoid. Scheme 65

CODE 75, TRANSMISSION VOLTAGE LOW

Note. Test numbers refer to numbers on diagnostic chart.

1. Checks for normal battery voltage of 9-15 volts.
2. Checks if low voltage is due to generator voltage supply circuit, or PCM. If voltage is less than 9 volts, PCM is okay.

If code sets when an accessory is operated, check for poor connections or excessive current draw. Also, check for poor connections at starter solenoid or fusible link.

Code 75 Schematic (Caprice) Transmission Voltage Low. Scheme 66

Code 75 Diagnostic Flow Chart (Caprice) Transmission Voltage Low. Scheme 67

CODE 77, PRIMARY COOLING FAN DRIVER

Cooling fan relay is supplied voltage when ignition is on. PCM controls solenoid valve by providing a ground through one of its Quad-Driver Modules (QDM). When relay is actuated, terminal is grounded and its monitored voltage will be low. When an output is off, its terminal voltage will be high. Each QDM has a separate fault line to indicate presence of a current fault to control module central processor.

Note. Test numbers refer to numbers on diagnostic chart.

1. Even if the fan does not operate, listen for an audible click from relay.
2. 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.
3. The remaining checks will identify a circuit problem that has caused an excessive current flow or inoperative relay.

Check related harness connectors, including PCM harness. Check for damaged or pushed out terminals.

Code 77 Schematic (Caprice) Primary Cooling Fan Driver. Scheme 68

Code 77 Diagnostic Flow Chart (Caprice) Primary Cooling Fan Driver. Scheme 69

CODE 78, SECONDARY COOLING FAN DRIVER

Cooling fan relay is supplied voltage when ignition is on. PCM controls solenoid valve by providing a ground through one of its Quad-Driver Modules (QDM). When relay is actuated, terminal is grounded and its monitored voltage will be low. When an output is off, its terminal voltage will be high. Each QDM has a separate fault line to indicate presence of a current fault to control module central processor.

Note. Test numbers refer to numbers on diagnostic chart.

1. Even if the fan does not operate, listen for an audible click from relay.
2. 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.
3. The remaining checks will identify a circuit problem that has caused an excessive current flow or inoperative relay.

Check related harness connectors, including PCM harness. Check for damaged or pushed out terminals.

Code 78 Diagnostic Flow Chart (Caprice) Secondary Cooling Fan Driver. Scheme 70

CODE 79, TRANSMISSION FLUID OVERTEMP

PCM supplies and monitors a 5-volt reference to sensor. As transmission temperature changes, sensor resistance changes, affecting monitored voltage. When fluid is cold, resistance is high, resulting in a high monitored voltage. When fluid is hot, resistance is low, resulting in a low monitored voltage. Code will set if transmission temperature is 120-130°C for 5 seconds and Codes 58 and 59 are not set.

Note. Test numbers refer to numbers on diagnostic chart.

1. Checks for out-of-calibration sensor or shorted circuit. 2 Simulates Code 59.

Check harness for potential short to ground. See Code 59 chart to check transmission temperature sensor temperature-to-resistance values. Also, check transmission fluid level. Check for conditions which could cause transmission to overheat i.e. trailer towing, steep grades, etc.

TEMPERATURE-TO-RESISTANCE VALUES (Measure resistance across sensor terminals)

Code 79 Diagnostic Flow Chart (Caprice) Transmission Fluid Overtemp. Scheme 71

CODE 81, 2-3 SHIFT SOLENOID

Voltage is supplied directly to solenoid. PCM controls solenoid by providing a ground circuit.

Note. Test numbers refer to numbers on diagnostic chart.

1. Checks 2-3 shift solenoid and internal transmission for shorts.
2. Checks for power to 2-3 shift solenoid from ignition through the fuse.

Check all connections at the transmission. An open in ignition feed circuit can cause multiple codes to set.

Code 81 Schematic (Caprice) 2-3 Shift Solenoid. Scheme 72

Code 81 Diagnostic Flow Chart (Caprice) 2-3 Shift Solenoid. Scheme 73

CODE 82, 1-2 SHIFT SOLENOID

Voltage is supplied directly to solenoid. PCM controls solenoid by providing a ground circuit for solenoid.

Note. Test numbers refer to numbers on diagnostic chart.

1. Checks 1-2 shift solenoid and internal transmission for shorts.
2. Checks for power to 1-2 shift solenoid from ignition through the fuse.

Check all connections at the transmission. An open in ignition feed circuit can cause multiple codes to set.

Code 82 Schematic (Caprice) 1-2 Shift Solenoid. Scheme 74

Code 82 Diagnostic Flow Chart (Caprice) 1-2 Shift Solenoid. Scheme 75

CODE 83, TCC PWM SOLENOID - A/T

PCM controls and monitors TCC PWM solenoid drive circuit. If voltage remains high when solenoid is commanded on or remains low when commanded off, code will set.

Note. Test numbers refer to numbers on diagnostic chart.

1. Checks if PCM is commanding TCC solenoid on.
2. Checks for voltage to solenoid.

Inspect harness connectors for backed out terminals, improper mating, broken locks, improperly formed or damaged terminals, poor terminal-to-wire connections or damaged harness. Perform intermittent check by monitoring circuit and code status while wiggling related wiring and connectors. If failure is induced, monitored circuit status will change rapidly and/or related code will set.

Code 83 Schematic (Caprice W/ A/T) TCC PWM Solenoid. Scheme 76

Code 83 Diagnostic Flow Chart (Caprice W/ A/T) TCC PWM Solenoid. Scheme 77

CODE 84, 3-2 CONTROL SOLENOID - WITH A/T

Note. Test numbers refer to numbers on diagnostic chart.

1. Checks 3-2 shift solenoid and internal transmission harness for shorts.
2. Checks for power to 3-2 shift solenoid from ignition through the fuse.

Check all connections at the transmission. An open in ignition feed circuit can cause multiple codes to set.

Code 84 Schematic (Caprice With A/T) 3-2 Control Solenoid. Scheme 78

Code 84 Diagnostic Flow Chart (Caprice With A/T) 3-2 Control Solenoid. Scheme 79

CODE 85, TCC STUCK ON

Note. Test numbers refer to numbers on diagnostic chart.

1. Checks mechanical state of TCC when PCM commands TCC solenoid off. TCC slip speed should increase.

Check for proper TP sensor operation. If TCC is mechanically stuck on, vehicle speed is zero, brakes are applied, and D2 is selected, TCC fluid will mechanically apply the TCC, causing an engine stall.

Code 85 Schematic (Caprice) TCC Stuck On. Scheme 80

Code 85 Diagnostic Flow Chart (Caprice) TCC Stuck On. Scheme 81

CODE 90, TCC SOLENOID CIRCUIT

Note. Test numbers refer to numbers on diagnostic chart.

1. Checks for a shorted internal transmission harness or TCC solenoid.
2. Checks power supply to TCC solenoid.

Check all connections to transmission pass-through connector. An open in the ignition feed circuit will cause multiple codes to set.

Code 90 Schematic (Caprice) TCC Solenoid Circuit. Scheme 82

Code 90 Diagnostic Flow Chart (Caprice) TCC Solenoid Circuit. Scheme 83

CODE 95, CHANGE OIL LIGHT

PCM monitors driving conditions and determines when to turn on change oil light. Maximum possible mileage accumulation is 7500 miles; however, PCM may turn on light sooner depending upon driving conditions (i.e. temperature and engine load history). Code will set and PCM will turn on light if wrong monitored voltage is present on light circuit for 26 seconds or more. PCM will not turn on SERVICE ENGINE SOON light.

Note. Test numbers refer to numbers on diagnostic chart.

1. Unplugging PCM will determine if circuit is shorted to ground or if PCM is at fault.

To reset oil light, turn ignition on with engine off. Cycle accelerator pedal from closed throttle to wide open throttle 3 times within 5 seconds. If light will not reset, check throttle angle. Throttle angle must go from less than 7.5 percent to greater than 75 percent for reset to occur. If this cannot be obtained, check for binding linkage, cable or throttle shaft. Service as necessary.

Code 95 Schematic (Caprice) Change Oil Light. Scheme 84

Code 95 Diagnostic Flow Chart (Caprice) Change Oil Light. Scheme 85

CODE 96, LOW OIL LIGHT

Code will set and PCM will turn on light if wrong monitored voltage is present on light circuit for 26 seconds or more. PCM will not turn on SERVICE ENGINE SOON light.

Note. Test numbers refer to numbers on diagnostic chart.

1. Unplugging PCM will determine if circuit is shorted to ground or if PCM is at fault.

Inspect harness and all related connections, including PCM connections. These may cause an intermittent code to set.

Code 96 Schematic (Caprice) Low Oil Light. Scheme 86

Code 96 Diagnostic Flow Chart (Caprice) Low Oil Light. Scheme 87

CODE 97, VSS OUTPUT CIRCUIT

Note. Test numbers refer to numbers on diagnostic chart.

1. Disable Traction Control (TC) system (if equipped) prior to this step. Switch is located in glove box. Whenever ignition is cycled off and then on, TC system will default to on. If vehicle speed is indicated at this point, code is intermittent.
2. Use Jumper Harness (J 35616-A) to prevent damage to harness.

Inspect harness and all related connections, including PCM connections.

Code 97 Diagnostic Flow Chart (Caprice) VSS Output Circuit. Scheme 88

SUMMARY

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

4.3L (VIN W) PCM Wiring Diagram (1 Of 3). Scheme 89

4.3L (VIN W) PCM Wiring Diagram (2 Of 3). Scheme 90

4.3L (VIN W) PCM Wiring Diagram (3 Of 3). Scheme 91

See also:
• BASIC TESTING
• TESTS W/O CODES
• SYSTEM/COMPONENT TESTS - 4.3L
• HARD OR INTERMITTENT TROUBLE CODE DETERMINATION
• DATA LINK CONNECTOR (DLC) TEST TERMINALS
• SCAN TESTER USAGE
• SCAN DATA
• CODE 11
• CODE 13
• CODE 14
• CODE 15
• CODE 16
• CODE 18
• CODE 21
• CODE 22
• CODE 23
• CODE 24
• CODE 25
• CODE 26
• CODE 27
• CODE 28
• CODE 29
• CODE 32
• CODE 33
• CODE 34
• CODE 36
• CODE 37
• CODE 38
• CODE 41
• CODE 42
• CODE 43
• CODE 44
• CODE 45
• CODE 46
• CODE 47
• CODE 48
• CODE 50
• CODE 52
• CODE 53
• CODE 55
• CODE 55
• CODE 58
• CODE 59
• CODE 63
• CODE 64
• CODE 65
• CODE 66
• CODE 67
• CODE 68
• CODE 69
• CODE 70
• CODE 72
• CODE 73
• CODE 75
• CODE 77
• CODE 78
• CODE 79
• CODE 81
• CODE 82
• CODE 83
• CODE 84
• CODE 85
• CODE 90
• CODE 95
• CODE 96
• CODE 97
• CLEARING TROUBLE CODES