Engine Controls Self-Diagnostics - 3.4L: Other Chevrolet Venture I

Hard Failures

Most hard failures cause MIL to illuminate and remain on until malfunction is repaired. If MIL illuminates and remains on (light may flash) during vehicle operation, cause of malfunction must be determined. See DIAGNOSTIC PROCEDURE .

If a sensor fails, PCM 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 MIL to flicker or glow and turn off about 10 seconds after intermittent fault goes away. Corresponding DTC, however, will be retained in PCM memory. If related fault does not reoccur within 50 engine starts, DTC will be erased from PCM memory. Intermittent failures may be caused by sensor, connector or wiring related problems. See INTERMITTENTS in appropriate TROUBLE SHOOTING - NO CODES article.

MALFUNCTION INDICATOR LIGHT INOPERATIVE

Note. After any repairs are completed, perform On-Board Diagnostic (OBD) system check. See ON-BOARD DIAGNOSTIC SYSTEM CHECK .

1. Perform On-Board Diagnostic (OBD) system check. See «ON-BOARD DIAGNOSTIC SYSTEM CHECK»(ref-9296-S00397014642000101600000) . After performing OBD system check, go to next step.
2. Attempt to start engine. If engine starts, go to next step. If engine does not start, go to step 6 .
3. Check instrument cluster ignition feed fuse. If fuse is okay, go to next step. If fuse is open, go to step 15 .
4. Turn ignition on. Using a test light connected to ground, backprobe ignition feed circuit at instrument cluster harness connector . See «WIRING DIAGRAMS»(ref-5022) article. If test light illuminates, go to next step. If test light does not illuminate, go to step 12 .
5. Turn ignition off. Disconnect PCM harness connectors. Turn ignition on. Using a fused jumper wire, jumper MIL driver circuit at PCM harness connector to ground. See «WIRING DIAGRAMS»(ref-5022) article. If MIL illuminates, go to step 10 . If MIL does not illuminate, go to step 11 .
6. Check PCM ignition feed and battery feed fuses. If fuses are okay, go to next step. If fuses are open, go to step 14 .
7. Turn ignition off. Disconnect PCM harness connectors. Turn ignition on. Using a test light connected to ground, probe ignition feed circuit at PCM harness connector. See «WIRING DIAGRAMS»(ref-5022) article. If test light illuminates, go to next step. If test light does not illuminate, go to step 13 .
8. Using a test light connected to ground, probe battery feed circuit at PCM harness connector. See «WIRING DIAGRAMS»(ref-5022) article. If test light illuminates, go to next step. If test light does not illuminate, go to step 13 .
9. Check for poor PCM ground or PCM ground connection. Repair as necessary. If ground and ground connection are okay, go to next step.
10. Check for poor PCM harness connection. Repair as necessary. If connection is okay, go to step 16 .
11. Check for open in Malfunction Indicator Light (MIL) driver circuit. See «WIRING DIAGRAMS»(ref-5022) article. Repair as necessary. If circuit is okay, go to step 17 .
12. Repair open in ignition feed circuit to instrument cluster. Repair as necessary.
13. Locate and repair open in PCM battery feed circuit or PCM ignition feed circuit. Repair as necessary.
14. Locate and repair short to ground in PCM battery feed circuit or PCM ignition feed circuit. Repair as necessary.
15. Locate and repair short to ground in instrument cluster ignition feed circuit. Repair as necessary.
16. Replace PCM. Perform PCM relearn procedures.
17. Check MIL driver circuit for poor connection at instrument cluster. Repair as necessary. If connection is okay, diagnose instrument cluster.

SUMMARY

If no hard fault codes are present, driveability symptoms exist or intermittent DTC(s) exist, proceed to appropriate TROUBLE SHOOTING - NO CODES article for diagnosis by symptom (i.e., ROUGH IDLE, NO START, etc.) or intermittent diagnostic procedures.