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Diagnostic Procedures

WARNING: This page is about a different car, the 2003 GMC Sierra, 2003 GMC Cab & Chassis Sierra, 2003 Chevrolet Silverado, and 2003 Chevrolet Cab & Chassis Silverado. However, it is still accessible from the selected car via links, so may be relevant.
  1. Perform Diagnostic System Check - Engine Controls. See DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROL under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS - 6.6L SIERRA & SILVERADO - DIESEL article. After performing Diagnostic System Check - Engine Controls, go to next step.
  2. Turn ignition on, with engine off. Remove underhood fuse/relay block cover. Using a test light connected to ground, probe the following fuses: INJ "B" fuse, FUEL HT fuse and SBA fuse (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  9 .
  3. Turn ignition off. Using test light connected to ground, probe both test points of the 25-amp INJ "B" fuse. Does the test light illuminate on either test point of the fuse? If yes, go to next step. If no, go to step  24 .
  4. Turn ignition off. Remove the ignition relay from the underhood fuse/relay. Using test light connected to battery voltage, probe the coil ground circuit of the ignition relay. Does the test light illuminate? If yes, go to next step. If no, go to step  7 .
  5. Turn ignition off. Disconnect negative battery cable at the battery. Disconnect the underhood fuse/relay block electrical connector that contains the ground wire for the ignition relay. Disconnect ECM electrical connector that contains the ground wire for the ignition relay. Test the coil ground wire of the ignition relay for a short to ground. Did you find and correct the condition? If yes, go to step  24 . If no, go to next step.
  6. Test the ignition relay coil ground bus bar circuit of the underhood fuse/relay block for a short to ground. Did you find a condition? If yes, go to step  23 . If no, go to next step.
  7. Test the relay load bus bar circuit of the underhood fuse/relay block between the 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  23 . If no, go to next step.
  8. Turn ignition off. Remove INJ "B" fuse, FUEL HT fuse and SBA fuse (if equipped) from the underhood fuse/relay block. Using test light connected to ground, probe all these fuse terminals. Does the test light illuminate at any of the fuse terminals? If yes, diagnose electrical system. If no, go to step  21 .
  9. Turn ignition on, with engine off. Probe both test points of the 20-amp ECM "B" fuse in the underhood fuse/relay block with test light connected to a good ground. Does the test light illuminate on both test points of the fuse? If yes, go to step  13 . If no, go to next step.
  10. Does test light illuminate on one test point of the 20-amp ECM "B" fuse? If yes, go to next step. If no, go to step  12 .
  11. Test the battery positive voltage bus bar circuit of the underhood fuse/relay block between the 20-amp ECM "B" fuse and the 15-amp INJ "B" fuse for a short to ground. Did you find a condition? If yes, go to step  23 . If no, go to step  21 .
  12. 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  23 . If no, diagnose electrical system.
  13. Turn ignition off. Remove ignition relay from the 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  23 .
  14. Turn ignition on. 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 next step. If no, go to step  23 .
  15. Turn ignition on, with engine off. Probe coil ground circuit of ignition relay at underhood fuse/relay block with a test light connected to a battery positive voltage. Does test light illuminate? If yes, go to step  18 . If no, go to next step.
  16. Turn ignition off. Disconnect negative battery cable at the battery. Disconnect the underhood fuse/relay block electrical connector that contains the ground wire for the ignition relay. Disconnect ECM electrical connector that contains the ground wire for the ignition relay. Test coil ground wire of ignition relay for a high resistance or an open. Did you find and correct the condition? If yes, go to step  24 . If no, go to next step.
  17. Test ignition relay coil ground bus bar circuit of the underhood fuse/relay block for a high resistance or an open. Did you find a condition? If yes, go to step  23 . If no, go to step  20 .
  18. 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. Using a test light connected to ground, probe INJ "B" fuse, HT FUEL fuse and SBA fuse (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  23 .
  19. 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  23 . If no, go to step  21 .
  20. Test for an intermittent and for a poor connection at the ECM connectors. Did you find a condition? If yes, go to step  24 . If no, go to step  22 .
  21. Replace ignition relay. After replacing relay, go to step  24 .
  22. Replace ECM. See ENGINE CONTROL MODULE under COMPUTERIZED ENGINE CONTROLS in REMOVAL & INSTALLATION - SIERRA & SILVERADO - DIESEL article. Reprogram ECM. After repairs, go to step  24 .
  23. Replace the underhood fuse/relay block assembly. After repairs, go to next step.
  24. 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, refer to NO-START - ENGINE CRANKS OKAY under NO-START DIAGNOSIS in BASIC DIAGNOSTIC PROCEDURES - 6.6L SIERRA & SILVERADO - DIESEL article.
  25. Clear DTCs with scan tool. Operate vehicle for 5 minutes. Does a DTC set during this ignition cycle? If yes, diagnose affected DTC(s). See DIAGNOSTIC TROUBLE CODE DEFINITIONS in SELF-DIAGNOSTICS - 6.6L SIERRA & SILVERADO - DIESEL article. If no, system is okay.
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