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Diagnostic Procedures

WARNING: This page is about a different car, the 2003 GMC Sierra and 2003 Chevrolet Silverado. However, it is still accessible from the selected car via links, so may be relevant.
  1. Perform diagnostic system check. See DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS - 4.3L SIERRA & SILVERADO article. After performing diagnostic system check, go to next step.
  2. Turn ignition on, with engine off. Remove underhood fuse/relay block cover. Probe the following fuses with a test light connected to a good ground: PCM 1, ETC/ECM, INJ 1, INJ 2, and SBA fuses, if equipped. See Figure . Does test light illuminate on at least one test point of each fuse? If yes, go to next step. If no, go to step  10 .
  3. Turn ignition off. Probe both test points of the PCM 1 fuse with 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  30 .
  4. Turn ignition off. Remove ignition relay from the underhood fuse/relay block. Probe ignition 1 voltage circuit of the ignition relay at the underhood fuse/relay block with a test light connected to a good ground. Does test light illuminate? If yes, go to step  7 . If no, go to next step.
  5. Test the relay load bus bar of the underhood fuse/relay block between ignition relay and fuses to the circuit components for a short to battery positive voltage. Did you find a condition? If yes, go to step  29 . If no, go to next step.
  6. Turn ignition off. Remove the following fuses from the underhood fuse/relay block: PCM 1, ETC/ECM, INJ 1, INJ 2 and SBA, if equipped. Probe the fuse terminals in the underhood fuse/relay block with a test light that is connected to a good ground. Does the test light illuminate at any of the fuse terminals? If yes, diagnose engine electrical system. If no, go to step  27 .
  7. Turn ignition off. Disconnect negative battery cable. Disconnect underhood fuse/relay block electrical connector that contains the ignition 1 voltage circuit for the ignition relay. Disconnect ignition switch electrical connector that contains the ignition 1 voltage circuit for ignition relay. Reconnect negative battery cable. Test the ignition 1 voltage circuit for a short to battery positive voltage. Did you find and correct the condition? If yes, go to step  30 . If no, go to next step.
  8. Turn ignition off. Probe ignition 1 voltage terminal on ignition switch side of the ignition switch electrical connector with a test light connected to a good ground. Does the test light illuminate? If yes, go to step  28 . If no, go to next step.
  9. Test the ignition 1 voltage bus bar circuit in the underhood fuse/relay block for a short to battery positive voltage. Did you find a condition? If yes, go to step  29 . If no, go to step  27 .
  10. Turn ignition off. Inspect the 40-amp IGN "B" fuse in the underhood fuse/relay block. Is fuse open? If yes, go to next step. If no, go to step  18 .
  11. Remove the 40-amp IGN "B" fuse from the underhood fuse/relay block. Probe both fuse terminals in the underhood fuse/relay block with a test light that is connected to a good ground. Does the test light illuminate on at least one fuse terminal? If yes, go to next step. If no, go to step  17 .
  12. Test the ignition 1 voltage circuit between the ignition switch and the underhood fuse/relay block for a short to ground. Did you find and correct the condition? If yes, go to step  30 . If no, go to next step.
  13. Test the ignition switch assembly for a short to ground. Did you find a condition? If yes, go to step  28 . If no, go to next step.
  14. Test the battery positive voltage circuit between the underhood fuse/relay block and ignition switch for a short to ground. Did you find and correct the condition? If yes, go to step  30 . If no, go to next step.
  15. Test the battery positive voltage bus bar circuit of the underhood fuse/relay block between the 40-amp IGN "B" fuse and ignition switch for a short to ground. Did you find a condition? If yes, go to step  29 . If no, go to next step.
  16. Test the ignition 1 voltage bus bar circuit of the underhood fuse/relay block that contains the ignition relay for a short to ground. Did you find a condition? If yes, go to step  29 . If no, go to step  27 .
  17. Turn ignition off. Probe the mounting stud for the battery positive cable at the underhood fuse/relay block with a test light connected to a good ground. Does the test light illuminate? If yes, go to step  29 . If no, diagnose engine electrical system.
  18. Turn ignition off. Remove ignition relay from underhood fuse/relay block. Probe the battery positive voltage circuit of the ignition relay at the underhood fuse/relay block with a test light connected to a good ground. Does test light illuminate? If yes, go to next step. If no, go to step  29 .
  19. Turn ignition on, with engine off. Probe the ignition 1 voltage circuit of the ignition relay at the underhood fuse/relay block with a test light connected to a good ground. Does the test light illuminate? If yes, go to step  23 . If no, go to next step.
  20. Turn ignition off. Test the ignition 1 voltage circuit between the ignition switch and the underhood fuse/relay block for a high resistance or for an open. Did you find and correct the condition? If yes, go to step  30 . If no, go to next step.
  21. Test the ignition switch assembly for a high resistance or for an open. Did you find a condition? If yes, go to step  28 . If no, go to next step.
  22. Test the battery positive voltage circuit between the ignition switch and the underhood fuse/relay block for a high resistance or for an open. Did you find and correct the condition? If yes, go to step  30 . If no, go to step  29 .
  23. Turn ignition on, with engine off. Probe the coil ground circuit of the ignition relay at the underhood fuse/relay block with a test light connected to battery voltage. Does test light illuminate? If yes, go to step  25 . If no, go to next step.
  24. Turn ignition off. Disconnect negative battery cable at battery. Disconnect the underhood fuse/relay block electrical connectors. Test the coil ground circuit of the ignition relay at the underhood fuse/relay block electrical connector for a high resistance or for an open. Did you find and correct the condition? If yes, go to step  30 . If no, go to step  29 .
  25. Turn ignition off. Jumper the ignition relay battery positive voltage circuit and ignition relay load circuit together at the underhood fuse/relay block with a 20-amp fused jumper wire. Probe the following fuses with a test light that is connected to a good ground: PCM 1, ETC/ECM, INJ 1, INJ 2 and SBA, if equipped. 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  29 .
  26. Test for an intermittent and for a poor connection at the underhood fuse/relay block, ignition relay connector location. Did you find a condition? If yes, go to step  29 . If no, go to next step.
  27. Replace ignition relay. After replacing relay, go to step  30 .
  28. Replace ignition switch. After replacing ignition switch, go to step  30 .
  29. Replace underhood fuse/relay block. After replacing fuse/relay block, go to next step.
  30. Replace any open fuses. Turn ignition off for 30 seconds. Attempt to start the engine. Does the engine start and run? If yes, go to next step. If no, go to NO-START - ENGINE CRANKS OKAY under NO-START in BASIC DIAGNOSTIC PROCEDURES - 4.3L SIERRA & SILVERADO article.
  31. Clear DTCs with a scan tool. Turn ignition off for 30 seconds. Start engine. Let engine reach operating temperature. Are re any DTCs that have not been diagnosed? If yes, diagnose affected DTC(s). See DIAGNOSTIC TROUBLE CODE DEFINITIONS in SELF-DIAGNOSTICS - 4.3L SIERRA & SILVERADO article. If no DTC(s) are set, system is okay.
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