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Home >> GMC >> 1998 >> Forward Control 4.3 W, Standard >> Repair and Diagnosis >> Engine Performance >> System >> Engine Control System - Tests W/Codes - Introduction >> Self-Diagnostic System >> On-Board Diagnostic (OBD) System Check >> 1.9L (VIN 7 & 8)

1.9L (VIN 7 & 8)

  1. Turn ignition off. Install scan tool and follow scan tool manufacturer's instructions to proceed with test. Turn ignition on. If scan tool displays PCM data, go to next step. If scan tool does not display PCM data, go to step  4.
  2. Attempt to start engine. If engine starts, go to next step. If engine does not start, see NO START DIAGNOSIS in appropriate BASIC DIAGNOSTIC PROCEDURES article.
  3. If DTCs are present, diagnose DTCs. See DIAGNOSTIC TESTS in appropriate TESTS W/CODES article. If DTCs are not present, observe scan tool data to determine if parameters are in correct operating range.
  4. Attempt to start engine. If engine starts, go next step. If engine does not start, go to step  12.
  5. If engine exhibits surge, rough idle or starts and then stalls, go to step  10. If engine runs okay, go to next step.
  6. Connect a test light between terminals No. 4 and No. 16 of DLC. See appropriate wiring diagram in WIRING DIAGRAMS article. If test light illuminates, go to next step. If test light does not illuminate, repair ground circuit.
  7. Check for open or shorted CLASS II DATA BUS circuit between DLC and PCM, and also between PCM and ABS module if equipped with ABS. Repair as necessary. If circuit is okay, go to next step.
  8. If vehicle is equipped with ABS, go to next step. If vehicle is not equipped with ABS, PCM and/or connections are faulty. Repair as necessary.
  9. Disconnect ABS module harness connector. If scan tool communicates with PCM, replace ABS controller. If scan tool does not communicate with PCM, PCM and/or connections are faulty. Repair as necessary.
  10. Turn ignition off. Disconnect 24-pin PCM harness connector. Turn ignition on with ignition off. If scan tool communicates with PCM, go to next step. If scan tool does not communicate with PCM, go to step  6.
  11. Check the following circuits at PCM for a short to battery positive. See appropriate wiring diagram in WIRING DIAGRAMS article.
    • EVO low circuit (Brown wire).
    • ECT sensor signal circuit (Yellow wire).
    • TP sensor 5-volt reference circuit (Gray wire).
    • TP sensor signal circuit (Dark Blue wire).
    • EST circuit for cylinders No. 1 and 4 (White wire).
    • EST circuit for cylinders No. 2 and 3 (Orange wire).

    Repair as necessary. If all circuits are okay, replace PCM.

  12. Turn ignition on. Using a test light connected to ground, probe both sides of PCM 1 and PCM B fuses (10-amp), located in underhood fuse block. If test light illuminates at both sides of both fuses, go to next step. If test light does not illuminate at both sides of both fuses, go to step  15.
  13. Turn ignition off. Disconnect 32-pin PCM harness connector. Turn ignition on. Using DVOM, measure voltage between ground and ignition positive feed and battery positive feed circuits at PCM harness connector. See appropriate wiring diagram in WIRING DIAGRAMS article. If battery voltage is present at each circuit, go to next step. If battery voltage is not present at each circuit, repair open or short in circuits between underhood fuse block and PCM.
  14. Check all PCM ground circuits. See appropriate wiring diagram in WIRING DIAGRAMS article. If all ground circuits are okay, PCM and/or connections are faulty. Repair as necessary.
  15. Repair ignition positive feed and battery positive feed circuits to underhood fuse block. Replace fuse as necessary.
  16. Repair open in faulty circuit between underhood fuse block and PCM.
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