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HOMESERVICE MANUALSGMC1999FORWARD CONTROL 5.7 R, AUTOMATICREPAIR AND DIAGNOSISEXTERNAL PAGESDIFFERENT CARSECTION 271 (ENGINE CONTROLS - SYSTEM & COMPONENT TESTING - 3.8L)RELAYS & SOLENOIDSIGNITION RELAY (REGAL)DIAGNOSTIC PROCEDURE
1999 GMC Forward Control 5.7 R, Automatic

Diagnostic Procedure

1999 GMC Forward Control 5.7 R, AutomaticSECTION Diagnostic Procedure
WARNING: This page does not describe the selected car, but rather 7 other vehicles, including the 2003 Pontiac Grand Prix, 2003 Pontiac Bonneville, 2003 Chevrolet Monte Carlo, 2003 Chevrolet Impala, and 2003 Buick Regal. However, it is still accessible from the selected car via links, so may be relevant.
NOTE: The ignition relay diagnostic procedure assumes that the vehicle battery is fully charged.
  1. Perform Diagnostic System Check - Engine Controls. See DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS - 3.8L BONNEVILLE, GRAND PRIX, IMPALA, LESABRE, MONTE CARLO, PARK AVENUE & REGAL article. After performing Diagnostic System Check - Engine Controls, go to next step.
  2. Turn ignition switch to RUN position, engine OFF. Remove the underhood junction block cover. Probe the following fuses using the test light connected to a good ground:
    • OXY SEN
    • ELEK IGN
    • F/INJ
    • TRANS
    • ENG EMIS

    Does the test light illuminate on at least one test point of each fuse? If yes, go to next step. If no, go to step  11.

  3. Turn ignition switch to OFF position. Probe both test points of the ENG EMIS fuse using a test light connected to a good ground. Does the test light illuminate on either test point of the fuse? If yes, go to next step. If no, go to step  36.
  4. Turn ignition switch to OFF position. Remove the ignition relay from the underhood junction block using Relay Puller Pliers (J 43244). Probe both test points of the PCM, BCM, U/H relay fuse in the Instrument Panel (IP) fuse block using a test light connected to a good ground. Does the test light illuminate on any of the fuse test points? If yes, go to step  8. If no, go to next step.
  5. Check the ignition relay load circuit bus bar of the underhood junction block between the ignition relay and the fuses to the circuit components for a short to battery positive voltage. Did you find a condition? If yes, go to step  35. If no, go to next step.
  6. Turn ignition switch to OFF position. Remove the following fuses from the underhood junction block:
    • OXY SEN
    • ELEK IGN
    • F/INJR
    • TRANS
    • ENG EMIS

    Probe all these fuse terminals in the underhood junction block using a test light that is connected to a good ground. Does the test light illuminate at any of the fuse terminals? If yes, go to next step. If no, go to step  34.

  7. Turn ignition switch to OFF position. Remove the A/C clutch relay from the underhood junction block using the relay puller pliers. Probe both fuse terminals of the ENG EMIS fuse in the underhood junction block using a test light connected to a good ground. Does the test light illuminate on either fuse terminal? If yes, diagnose engine electrical circuit problem. See ENGINE ELECTRICAL DIAGNOSTIC SYSTEM CHECK under SELF-DIAGNOSTIC SYSTEM in appropriate GENERATORS & REGULATORS article. If no, go to step  34.
  8. Turn ignition switch to OFF position. Disconnect the ignition switch harness connector. Connect a 20-amp fused jumper wire from the battery positive voltage circuit terminal at the ignition switch connector, to the corresponding terminal at the vehicle harness connector. Probe the ignition 1 voltage circuit at the ignition switch harness connector using a test light connected to a good ground. Does the test light illuminate? If yes, go to step  33. If no, go to next step.
  9. Remove the following fuses from the I/P fuse block:
    • TURN SIGNALS, CORN LPS
    • AIR BAG
    • CLUSTER
    • PCM, BCM, U/H RELAY

    Probe the ignition switch harness connector ignition 1 voltage circuit that leads to the IP fuse block, using a test light connected to a good ground. Does the test light illuminate? If yes, go to step  30. If no, go to next step.

  10. Turn ignition switch to OFF position. Disconnect the harness connector at the underhood junction block that contains the ignition 1 voltage circuit of the ignition relay. Probe the ignition relay ignition 1 voltage circuit at the underhood junction block vehicle harness electrical connector using a test light connected to a good ground. Does the test light illuminate? If yes, go to step  31. If no, go to step  35.
  11. Turn ignition switch to OFF position. Probe both test points of the IGN 1 fuse (30-amp) in the underhood junction block using a test light connected to a good ground. Does the test light illuminate on both test points of the fuse? If yes, go to step  15. If no, go to next step.
  12. Does the test light illuminate on one test point of the IGN 1 (30-amp) fuse? If yes, go to next step. If no, go to step  21.
  13. Check the battery positive voltage circuit between the underhood junction block and the ignition switch for a short to ground. Did you find and correct the condition? If yes, go to step  36. If no, go to next step.
  14. Check the ignition 1 voltage circuit between the ignition switch and the PCM/ECM, BCM, U/H relay fuse terminals in the IP fuse block for a short to ground. Did you find and correct the condition? If yes, go to step  36. If no, go to step  33.
  15. Turn ignition switch to RUN position, engine OFF. Probe both test points of the PCM/ECM, BCM, U/H relay fuse using a test light connected to a good ground. Does the test light illuminate on both test points of the fuse? If yes, go to step  22. If no, go to next step.
  16. Does the test light illuminate on one test point of the PCM, BCM, U/H relay fuse? If yes, go to step  19. If no, go to next step.
  17. Check the ignition 1 voltage circuit between the ignition switch and the PCM, BCM, U/H relay fuse for a high resistance or for an open. Did you find and correct the condition? If yes, go to step  36. If no, go to next step.
  18. Check the battery positive voltage circuit between the underhood junction block and the ignition switch for a high resistance or for an open. Did you find and correct the condition? If yes, go to step  36. If no, go to step  33.
  19. Check the ignition 1 voltage circuit between the IP fuse block and the underhood junction block for a short to ground. Did you find and correct the condition? If yes, go to step  36. If no, go to next step.
  20. Check the underhood junction block, ignition 1 voltage bus bar circuit to the ignition relay for a short to ground. Did you find and correct the condition? If yes, go to step  35. If no, go to step  32.
  21. Turn ignition switch to OFF position. Probe the mounting stud for the battery positive cable at the underhood junction block using a test light connected to a good ground. Does the test light illuminate? If yes, go to step  35. If no, diagnose engine electrical circuit problem. See ENGINE ELECTRICAL DIAGNOSTIC SYSTEM CHECK under SELF-DIAGNOSTIC SYSTEM in appropriate GENERATORS & REGULATORS article.
  22. Turn ignition switch to OFF position. Remove the ignition relay using the relay puller pliers, from the underhood junction block. Probe the ignition relay battery positive voltage circuit at the underhood junction block using a test light connected to a good ground. Does the test light illuminate? If yes, go to next step. If no, go to step  35.
  23. Turn ignition switch to RUN position, engine OFF. Probe the ignition relay ignition 1 voltage circuit at the underhood junction block using a test light connected to a good ground. Does the test light illuminate? If yes, go to step  25. If no, go to next step.
  24. Check the ignition 1 voltage circuit between the I/P fuse block and the underhood junction block for a high resistance or for an open. Did you find and correct the condition? If yes, go to step  36. If no, go to step  35.
  25. Turn ignition switch to RUN position, engine OFF. Probe the ignition relay coil ground circuit at the underhood junction block using a test light connected to battery voltage. Does the test light illuminate? If yes, go to step  27. If no, go to next step.
  26. Turn ignition switch to OFF position. Disconnect the negative battery cable at the battery. Disconnect the underhood junction block harness connector that contains the relay coil ground circuit. Check the ignition relay coil ground circuit at the underhood junction block harness connector for a high resistance or for an open. Did you find and correct the condition? If yes, go to step  36. If no, go to step  35.
  27. Turn ignition switch to OFF position. Jumper the ignition relay battery positive voltage circuit and the ignition relay load circuit together at the underhood junction block using a 20-amp fused jumper wire. Probe the following fuses using a test light connected to a good ground:
    • OXY SEN
    • ELEK IGN
    • F/INJR
    • TRANS
    • ENG EMIS

    Does the test light illuminate on at least one test point of each fuse? If yes, go to next step. If no, go to step  35.

  28. Remove the A/C clutch relay from the underhood junction block using the relay puller pliers. Probe the A/C clutch relay ignition 1 voltage circuit using a test light that is connected to a good ground. Does the test light illuminate? If yes, go to next step. If no, go to step  35.
  29. Check for an intermittent and for a poor connection at the underhood junction block, ignition relay connector location. Did you find and correct the condition? If yes, go to step  35. If no, go to step  32.
  30. Repair the short to battery positive voltage in the ignition 1 voltage circuit between the ignition switch and the I/P fuse block. After repair, go to step  36.
  31. Repair the short to battery positive voltage in the ignition 1 voltage circuit between the I/P fuse block and the underhood junction block harness connector.
  32. Replace the ignition relay. After repair, go to step  36.
  33. Replace the ignition switch. After repair, go to step  36.
  34. Replace the A/C clutch relay. After repair, go to step  36.
  35. Replace the underhood electrical center. After repair, go to next step.
  36. Replace any open fuses. Turn ignition switch to OFF position for 30 seconds. Attempt to start the engine. Does the engine start and run? If yes, go to next step. If no, go to ENGINE CRANKS BUT DOES NOT RUN under NO START DIAGNOSTICS in BASIC DIAGNOSTICS - 3.8L BONNEVILLE, GRAND PRIX, IMPALA, LESABRE, MONTE CARLO, PARK AVENUE & REGAL article.
  37. Clear the DTCs using a scan tool. Operate the vehicle for 5 minutes. Does a DTC set during this ignition cycle? If yes, go to DIAGNOSTIC TROUBLE CODE DEFINITIONS in SELF-DIAGNOSTICS - 3.8L BONNEVILLE, GRAND PRIX, IMPALA, LESABRE, MONTE CARLO, PARK AVENUE & REGAL article. If no, go to next step.
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When to See a Mechanic

Stop DIY work and contact a certified mechanic immediately if any of the following apply:

  • • You smell fuel, burning insulation, or see smoke.
  • • Brakes feel soft, pull hard to one side, or make grinding noises.
  • • The engine overheats, stalls repeatedly, or misfires under load.
  • • You are missing required tools, torque specs, or safe lifting equipment.
  • • You are not confident in the next step or safety outcome.