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Home >> GMC >> 1996 >> Forward Control 4.3 Z, Automatic >> Repair and Diagnosis >> Engine Performance >> System >> Engine Controls - Basic Engine Testing - P Series (Diesel) >> On-Board Diagnostic (OBD) System Check >> A-1, Malfunction Indicator Light (Mil)

A-1, Malfunction Indicator Light (Mil)

  1. Perform ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK . 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 fuse No. 4 (Gauges). If fuse if faulty, go to step 14). If fuse is okay, go to next step.
  4. Turn ignition on. Using a test light connected to ground, probe ignition feed terminal at PCM connector. See Figure. If test light illuminates, go to step 5). If test light does not illuminate, go to step 14).
  5. Turn ignition off. Disconnect Black PCM harness connector. Turn ignition on. Using a fused jumper wire, jumper MIL control circuit at PCM connector terminal (Brown/White wire). See Figure. If MIL illuminates, go to step 9). If test light does not illuminate, go to step 10).
  6. Check fuses to PCM ignition and battery feed circuit. See Figure. If fuses are okay, go to next step. If fuse(s) are faulty, go to step 13).
  7. Turn ignition off. Disconnect PCM connectors. Turn ignition on. Using a test light connected to ground, probe PCM harness connector ignition and battery feed circuits. See Figure. If test light illuminates on both circuits, go to next step. If test light does not illuminate on both circuits, go to step 12).
  8. Check for faulty or poor PCM ground connections. Repair as necessary. After repairs, go to step 20). If ground connections are okay, go to next step.
  9. Check for poor connection at PCM harness connector. Repair as necessary. After repairs, go to step 20). If connector is okay, go to step 15).
  10. Check for open MIL control circuit. Repair as necessary. After repairs, go to step 20).
  11. Repair open in ignition feed circuit to instrument cluster. See Figure. After repairs, go to step 20).
  12. Locate and repair open in PCM battery feed or ignition circuit. Repair as necessary. After repairs, go to step 20).
  13. Locate and repair short to ground in PCM ignition feed circuit or PCM battery feed circuit. Repair as necessary. After repairs, go to step 20).
  14. Locate and repair short to ground in instrument cluster ignition feed circuit. After repairs, go to step 20).
  15. Replace PCM. Perform PCM relearn procedures. After repairs, go to step 20).
  16. Check for poor connection at MIL control circuit to instrument cluster connector. Repair as necessary. After repairs, go to step 20). If circuit is okay, go to next step.
  17. Remove instrument panel assembly. Inspect MIL bulb. If bulb is okay, go to step 19). If bulb is faulty, go to next step.
  18. Replace MIL bulb. After replacing bulb, go to step 20).
  19. Replace instrument cluster. After repairs, go to step 20).
  20. Using scan tool, select DTC, CLEAR INFO function. Attempt to start engine. If engine starts and continues to run, go to next step. If engine does not start or starts and dies/stalls, go to step 2).
  21. Warm engine to normal operating temperature. Using scan tool, select DTC, FAILED THIS IGN function. Diagnose any DTC present. See TESTS W/CODES article. If DTC(s) are not present, go to next step.
  22. Select CAPTURE INFO, REVIEW INFO function. If DTC(s) are present. Diagnose any DTC present. See TESTS W/CODES article.
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