Hard Failures
Hard failures cause Malfunction Indicator Light (MIL) to glow and remain on until problem 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. See CODE IDENTIFICATION table under TROUBLE CODE DEFINITION. If a sensor fails, Electronic Control Module (ECM) will use a substitute value in its calculations to continue engine operation. In this condition, commonly known as limp-in mode, vehicle runs but driveability will not be optimum.
Intermittent Failures
Intermittent failures may cause MIL to flicker or glow and go out after intermittent fault goes away. However, corresponding trouble code will be retained in ECM memory. If related fault does not reoccur within a certain time frame, related trouble code will be erased from ECM memory. Intermittent failures may be caused by a sensor, connector or wiring related problems. See INTERMITTENTS in the TESTS W/O CODES - 2.6L article.
RETRIEVING CODES
Note. Codes can also be retrieved using a scan tester. Trouble codes are also referred to as DTCs.
- Code retrieval starts with diagnostic circuit check. See «DIAGNOSTIC CIRCUIT CHECK»(ref-15942-S42922698022001122700000) chart under CODE CHARTS. MIL will come on when ignition is on and engine is not running. When engine is started, MIL should go off. If light remains on while engine is running, a trouble code is present.
- If light does not come on with ignition on and engine off, inspect MIL circuit before continuing. If MIL fails to operate, see «DIAGNOSTIC CIRCUIT CHECK»(ref-15942-S42922698022001122700000) chart.
- To retrieve codes, install jumper wire between ALDL diagnostic leads. (Scheme 8) Turn ignition on. Count number of flashes from MIL to identify code. (Scheme 9) For example, Code 12 will be flashed as follows: flash, pause, flash, flash.
- If system is operating properly, Code 12 should be displayed with ignition on and engine off, indicating diagnostic system is capable of storing codes. Code 12 will flash 3 times, followed by any stored trouble codes. Each code will be flashed 3 times starting with lowest code. Once all codes are displayed, cycle will repeat. After codes are retrieved, remove jumper wire from diagnostic leads to exit diagnostic mode.
Scheme 8
Scheme 9
CLEARING CODES
- After repairs are performed, clear ECM memory of all stored codes. Ensure ignition is off. To clear codes, remove fuse No. 3 from instrument panel fuse block, or remove 60-amp MAIN fuse located in engine compartment fuse block.
- Trouble codes can also be cleared by disconnecting negative battery cable. However, other memory functions (clock, radio, etc.) will need to be reset.
CODE CHARTS
Note. To identify ECM connector terminals, see ECM TERMINAL IDENTIFICATION chart. To test ECM power supply, go to TEST NO . 1 chart.
| Pin No. | Wire Color | Main Connection |
|---|---|---|
| 1 | Red | Power |
| 2 | Black/Green | Injector Ground |
| 3 | Black/Yellow | DLC (ALDL) |
| 4 | Blue/Yellow | Idle Input (WOT Switch) |
| 5 | Green/Black | AC Input |
| 6 | Not Used | |
| 7 | Green | CKP Sensor Signal |
| 8 | Green/White | Pressure Regulator Control |
| 9 | Not Used | 10 |
| Light Green | EGR Duty Solenoid | 11 |
| Not Used | 12 | White/Black |
| Injector No. 2 | 13 | White |
| Injector No. 1 | 14 | Red |
| Power | 15 | |
| Not Used | 16 | |
| Not Used | 17 | |
| Trans Input | 18 | Green/Black |
| Monitor | 19 | Green/Yellow |
| Monitor | 20 | White |
| CKP Sensor Reference | 21 | White/Green |
| EGR VSV | 22 | Green |
| MIL | 23 | Light Green/White |
| EVAP VSV | 24 | White/Blue |
| Injector No. 4 | 25 | White/Red |
| Injector No. 3 | 26 | Black/Green |
| Injector Ground |
ECM 26-PIN TERMINAL IDENTIFICATION
| Pin No. | Wire Color | Main Connection |
|---|---|---|
| 1 | Blue | Power Signal |
| 2 | Black/Red | Ground (Power, Ignition) |
| 3 | Green/Orange | MAP Sensor Reference |
| 4 | Red/White | Power (Backup) |
| 5 | White | Vehicle Speed Sensor |
| 6 | Shield | Oxygen Sensor |
| 7 | Black/White | ECT Sensor Ground |
| 8 | Brown/White | ECT Sensor Input |
| 9 | Blue/White | MAP Sensor Input |
| 10 | Not Used | |
| 11 | Black | Ground (Power) |
| 12 | Not Used | |
| 13 | Black/Red | Ground (Power, Ignition) |
| 14 | Red | Airflow Sensor (Power) |
| 15 | Green/Red | WOT Input (WOT Switch) |
| 16 | Yellow/Black | Starter Switch |
| 17 | Shield | Airflow Sensor |
| 18 | Blue/Red | MAP Sensor Ground |
| 19 | Black | Airflow Sensor Ground |
| 20 | Green | Oxygen Sensor Input |
| 21 | White | Airflow Sensor Input |
| 22 | Black | Ground (Power) |
ECM 22-PIN TERMINAL IDENTIFICATION
Scheme 10
| CAUTION | Perform all voltage measurements with ECM harness connector installed. Use a high-impedance voltmeter (10,000 ohm minimum). Verify battery voltage is greater than 11 volts. |
Scheme 11
Circuit Confirmation
- Disconnect ECM harness connectors.
- Turn ignition switch to ON position.
- Ensure battery voltage is present at terminals No. 1, 14 and 4.
- Ensure continuity exists between terminals No. 11 and 22.
CODE 12 - SYSTEM NORMAL
This DTC No. 12 is always displayed with the key "ON" and the engine not running and it only means that the engine is not running. This DTC No. 12 is not stored in memory.
Note. If the signal DTC No. 12 only is displayed when the function key is operated after clearing the memory. It indicates that the ECM electrical circuits and self diagnosis system are functioning normally.
Scheme 12
CODE 13 - HEATED OXYGEN SENSOR CIRCUIT
Note. See appropriate WIRING DIAGRAM in WIRING DIAGRAMS section for terminal and connector identification.
Note. Test numbers refer to numbers on diagnostic chart.
- This step checks AIR system operation: Idle engine at normal operating temperature. Stop engine. Disconnect AIR hose at check valve and plug check valve. Restart engine and idle, immediately check direction of airflow.
- This step tests continuity of oxygen sensor circuit (Green wire) between ECM 22-pin connector terminal No. 20 and oxygen sensor.
Scheme 13
CODE 14 - SHORTED ENGINE COOLANT TEMPERATURE SENSOR
Note. See appropriate WIRING DIAGRAM in WIRING DIAGRAMS section for terminal and connector identification.
Scheme 14
Scheme 15
CODE 15 - OPEN ENGINE COOLANT TEMPERATURE SENSOR
Note. See appropriate WIRING DIAGRAM in WIRING DIAGRAMS section for terminal and connector identification.
Scheme 16
CODE 21 - THROTTLE VALVE SWITCH (IDLE & FULL THROTTLE)
Note. See appropriate WIRING DIAGRAM in WIRING DIAGRAMS section for terminal and connector identification.
Scheme 17
Scheme 18
Scheme 19
CODE 22 - STARTER SIGNAL
Note. See appropriate WIRING DIAGRAM in WIRING DIAGRAMS section for terminal and connector identification.
Scheme 20
CODE 23, 35, 54 POWER TRANSISTOR CIRCUIT
Note. See appropriate WIRING DIAGRAM in WIRING DIAGRAMS section for terminal and connector identification.
Note. Test numbers refer to numbers on diagnostic chart.
- This step checks continuity of power transistor power circuit. Check continuity of ground at ECM terminal No. 13.
- Inspecting power transistor: Disconnect coil wire at distributor. Attach Spark Tester (J-125) or equivalent to free end of coil wire. Remove power transistor from bottom of intake manifold, and disconnect harness connector. Connect a 2-wire jumper lead between power transistor connector and power transistor. In one wire of jumper lead install a 1.5-volt dry cell battery with negative side of battery facing power transistor. Ground power transistor to frame and turn ignition on. Disconnect and reconnect jumper lead at power transistor connector. Verify spark exists at spark tester. If spark is not present, replace power transistor.
Scheme 21
CODE 25, 53 - FUEL PRESSURE REGULATOR VSV
Note. See appropriate WIRING DIAGRAM in WIRING DIAGRAMS section for terminal and connector identification.
Note. Test number refers to number on diagnostic chart.
- Test resistance between Red wire and Green/White wire at VSV connector.
Scheme 22
Scheme 23
CODE 26, 27 - CANISTER PURGE VSV
Note. See appropriate WIRING DIAGRAM in WIRING DIAGRAMS section for terminal and connector identification.
Note. Test number refers to number on diagnostic chart.
- Test resistance between Light Green/Red wire and Black/White wire at VSV connector.
Scheme 24
Scheme 25
CODE 32 - EGR SYSTEM MALFUNCTION
Note. See appropriate WIRING DIAGRAM in WIRING DIAGRAMS section for terminal and connector identification.
Note. Test numbers refer to numbers on diagnostic chart.
- Specified reappearance pattern: Run engine at idle and normal operating temperature. Keep vehicle at idle for more than 10 seconds at stop. Drive vehicle at 10 MPH. Accelerate to more than 30 MPH. After 10-30 seconds, decelerate to complete stop. Repeat pattern several times.
- This step checks EGR operation by re-applying signal vacuum.
Scheme 26
Scheme 27
Scheme 28
Scheme 29
CODE 33 - FUEL INJECTOR CIRCUIT (OPEN OR GROUNDED)
Note. See appropriate WIRING DIAGRAM in WIRING DIAGRAMS section for terminal and connector identification.
Scheme 30
CODE 34 - MAP SENSOR
Note. See appropriate WIRING DIAGRAM in WIRING DIAGRAMS section for terminal and connector identification.
Scheme 31
Scheme 32
CODE 41 - CRANKSHAFT POSITION SENSOR SIGNAL
Note. See appropriate WIRING DIAGRAM in WIRING DIAGRAMS section for terminal and connector identification.
Note. Test number refers to number on diagnostic chart.
- Inspecting Crankshaft Position (CKP) sensor circuit: Disconnect CKP sensor and ECM connectors. Turn ignition on. Measure CKP sensor voltage and resistance values. See CKP SENSOR SPECIFICATIONS table. If values are not within specification, repair or replace appropriate harness or connector. Reconnect CKP and ECM connectors.
| Between Terminals (1) | Resistance | Voltage |
|---|---|---|
| 20 & White | 0 | |
| 7 & Green | 0 | |
| Green/Black & Ground | 10-14 | |
| Black & Ground | 0 | |
| (1) Circuit numbers refer to ECM terminal numbers, and wire colors refer to CKP sensor wire colors at connector. | ||
| (1) | Circuit numbers refer to ECM terminal numbers, and wire colors refer to CKP sensor wire colors at connector. |
CKP SENSOR SPECIFICATIONS
Scheme 33
CODE 43, 65 - THROTTLE VALVE SWITCH
Note. See appropriate WIRING DIAGRAM in WIRING DIAGRAMS section for terminal and connector identification.
Scheme 34
CODE 44, 45 - OXYGEN SENSOR-LEAN/RICH FUEL MIXTURE
Note. See appropriate WIRING DIAGRAM in WIRING DIAGRAMS section for terminal and connector identification.
Note. Test numbers refer to numbers on diagnostic chart.
- Measure voltage at oxygen sensor connector.
- Jumper wire allows voltage measurement of circuit.
Scheme 35
Scheme 36
CODE 51, 52 - FAULTY ECM RAM/ROM
Note. See appropriate WIRING DIAGRAM in WIRING DIAGRAMS section for terminal and connector identification.
Note. Test number refers to number on diagnostic chart.
- Before replacing ECM, check circuit connections: Disconnect ECM harness connectors. Inspect all terminals and repair as necessary. Reconnect ECM harness connectors, and road test vehicle. Check for codes. If condition persists or code reappears, replace ECM.
Scheme 37
CODE 61, 62 - AIRFLOW SENSOR SIGNAL
Note. See appropriate WIRING DIAGRAM in WIRING DIAGRAMS section for terminal and connector identification.
Scheme 38
Scheme 39
CODE 63 - VEHICLE SPEED SENSOR SIGNAL
Note. See appropriate WIRING DIAGRAM in WIRING DIAGRAMS section for terminal and connector identification.
Code 63 can be set, without a system failure, under following conditions
- Auto. Trans. In Drive position, with brake pedal depressed and accelerator pedal depressed more than halfway for more than 3 seconds.
- Manual Trans. Under severe climbing conditions, with vehicle stationary, accelerator pedal depressed more than halfway for more than 3 seconds, and clutch partially engaged.
Note. Test numbers refer to numbers on diagnostic chart.
- Check for continuity between ECM 22-pin connector terminal No. 5 (White wire) and ground. Disconnect speedometer cable at transmission. Tester should pulsate between open and continuity as speedometer cable is rotated slowly. NOTE: Instrument cluster has two 12-pin connectors. Ensure appropriate wire color is tested.
- Ensure continuity exists on White wire between ECM 22-pin connector terminal No. 5 and instrument cluster 12-pin connector terminal No. 9. Ensure continuity exists on Black/White wire between instrument cluster 12-pin connector terminal No. 9 and ground.
- Remove instrument cluster assembly. Check continuity between terminals No. 1 and 2. Tester should pulsate between open and continuity as speedometer inner shaft is rotated slowly.
Scheme 40
Scheme 41
CODE 64 - FUEL INJECTOR CIRCUIT (ECM TRANSISTOR)
Note. See appropriate WIRING DIAGRAM in WIRING DIAGRAMS section for terminal and connector identification.
Scheme 42
SUMMARY
If no hard fault codes (or only pass codes) are present, driveability symptoms exist or intermittent codes exist, proceed to TESTS W/O CODES - 2.6L article for diagnosis by symptom (i.e., ROUGH IDLE, NO START, etc.) or intermittent diagnostic procedures.