LEMON Manuals: Even more car manuals for everyone: 1960-2025
Home >> Chevrolet >> 2003 >> Avalanche 2500, 4WD >> Repair and Diagnosis >> Engine Performance >> System >> Engine Controls - System & Component Testing - 8.1L >> Ignition Systems >> Ignition Relay >> Diagnostic Procedures
April 5, 2026: LEMON Manuals is launched! Read the announcement.

Diagnostic Procedures

  1. Perform diagnostic system check. See DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS under SELF DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS - 8.1L AVALANCHE, SIERRA, SILVERADO, SUBURBAN & YUKON XL article. After performing diagnostic system check, go to next step.
  2. Turn ignition on, with engine off. Remove underhood fuse/relay block cover. Probe following fuses with a test light connected to a good ground: PCM 1, ETC/ECM, INJ 1, INJ 2, and SBA fuse, 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 PCM 1 fuse with a test light connected to a good ground. Does test light illuminate on either test point of fuse? If yes, go to next step. If no, go to step  30 .
  4. Turn ignition off. Remove ignition relay from underhood fuse/relay block. Probe ignition 1 voltage circuit of ignition relay at 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 relay load bus bar of underhood fuse/relay block between ignition relay and fuses to 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 following fuses from underhood fuse/relay block: PCM 1, ETC/ECM, INJ 1, INJ 2 and SBA fuse, if equipped. Probe fuse terminals in underhood fuse/relay block with a test light that is connected to a good ground. Does test light illuminate at any of 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 ignition 1 voltage circuit for ignition relay. Disconnect ignition switch electrical connector that contains ignition 1 voltage circuit for ignition relay. Reconnect negative battery cable. Test ignition 1 voltage circuit for a short to battery positive voltage. Did you find and correct 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 ignition switch electrical connector with a test light connected to a good ground. Does test light illuminate? If yes, go to step  28 . If no, go to next step.
  9. Test ignition 1 voltage bus bar circuit in 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 40-amp IGN "B" fuse in underhood fuse/relay block. Is fuse open? If yes, go to next step. If no, go to step  18 .
  11. Remove 40-amp IGN "B" fuse from underhood fuse/relay block. Probe both fuse terminals in underhood fuse/relay block with a test light that is connected to a good ground. Does test light illuminate on at least one fuse terminal? If yes, go to next step. If no, go to step  17 .
  12. Test ignition 1 voltage circuit between ignition switch and underhood fuse/relay block for a short to ground. Did you find and correct condition? If yes, go to step  30 . If no, go to next step.
  13. Test 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 battery positive voltage circuit between underhood fuse/relay block and ignition switch for a short to ground. Did you find and correct condition? If yes, go to step  30 . If no, go to next step.
  15. Test battery positive voltage bus bar circuit of underhood fuse/relay block between 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 ignition 1 voltage bus bar circuit of underhood fuse/relay block that contains 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 mounting stud for battery positive cable at underhood fuse/relay block with a test light connected to a good ground. Does 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 battery positive voltage circuit of ignition relay at 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 ignition 1 voltage circuit of ignition relay at underhood fuse/relay block with a test light connected to a good ground. Does test light illuminate? If yes, go to step  23 . If no, go to next step.
  20. Turn ignition off. Test ignition 1 voltage circuit between ignition switch and underhood fuse/relay block for a high resistance or for an open. Did you find and correct condition? If yes, go to step  30 . If no, go to next step.
  21. Test 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 battery positive voltage circuit between ignition switch and underhood fuse/relay block for a high resistance or for an open. Did you find and correct condition? If yes, go to step  30 . If no, go to step  29 .
  23. Turn ignition on, with engine off. Probe coil ground circuit of ignition relay at 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 underhood fuse/relay block electrical connectors. Test coil ground circuit of ignition relay at underhood fuse/relay block electrical connector for a high resistance or for an open. Did you find and correct condition? If yes, go to step  30 . If no, go to step  29 .
  25. Turn ignition off. Jumper ignition relay battery positive voltage circuit and ignition relay load circuit together at underhood fuse/relay block with a 20-amp fused jumper wire. Probe following fuses with a test light that is connected to a good ground: PCM 1, ETC/ECM, INJ 1, INJ 2 and SBA fuse, if equipped. Does 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 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 engine. Does engine start and run? If yes, go to next step. If no, go to NO-START - ENGINE CRANKS OKAY under NO-START DIAGNOSIS in BASIC DIAGNOSTIC PROCEDURES - 8.1L AVALANCHE, SIERRA, SILVERADO, SUBURBAN & YUKON XL 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 - 8.1L AVALANCHE, SIERRA, SILVERADO, SUBURBAN & YUKON XL article. If no DTC(s) are set, system is okay.
scientia non olet · About LEMON Manuals