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Diagnostic Procedure

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  1. Perform Alternative Fuels Diagnostic System Check - Engine Controls. See ALTERNATIVE FUELS DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS under SELF-DIAGNOSTIC SYSTEM in appropriate SELF-DIAGNOSTICS article. After performing Alternative Fuels Diagnostic System Check - Engine Controls, go to next step.
  2. With scan tool, observe Alternative Fuels Engine Control Module (AF ECM) Diagnostic Trouble Code (DTC) information. Are DTCs P0201-P0208, or DTC P1650 set? If yes, go to DIAGNOSTIC TROUBLE CODE DEFINITIONS in appropriate SELF-DIAGNOSTICS article. If no, go to next step.
    3. NOTE: Verify adequate CNG fuel is in fuel tank before proceeding with this diagnostic test.
  3. Crank engine for 4 seconds. Does engine start and idle on all cylinders? If yes, go to DIAGNOSTIC AIDS . If no, go to next step.
  4. Inspect IGN E fuse. Is IGN E fuse open? If yes, go to next step. If no, go to step  9.
  5. Turn OFF the ignition. Disconnect both fuel injector relays. Disconnect alternative fuels fuel pump relay. Disconnect AF ECM harness connector C001. Probe ignition voltage circuit of fuel injector relays, at under hood bussed electrical center, with a test light connected to battery voltage. Is test light illuminated? If yes, go to step  17. If no, go to next step.
  6. Install a NEW IGN E fuse. Turn ON the ignition, with the engine OFF. Install fuel injector relays one at a time. Inspect IGN E fuse after each relay is installed. Does fuse open after either relay is installed? If yes, go to step  22. If no, go to next step.
  7. Install AF fuel pump relay. Inspect IGN E fuse. Is fuse open? If yes, go to step  23. If no, go to next step.
  8. Turn OFF the ignition. Install AF ECM harness connector C001. Turn ON the ignition, with the engine OFF. Inspect IGN E fuse. Is fuse open? If yes, go to step  24. If no, go to DIAGNOSTIC AIDS .
  9. Turn OFF the ignition. Disconnect both fuel injector relays. Turn ON the ignition, with the engine OFF. Probe ignition voltage circuit of both fuel injector relays with a test light connected to a known good ground. Does test light illuminate for both circuits? If yes, go to next step. If no, go to step  16.
  10. Probe battery voltage circuit of both fuel injector relays with a test light connected to a known good ground. Does test light illuminate for both circuits? If yes, go to step  13. If no, go to next step.
  11. Probe battery voltage circuit of circuit that did not illuminate test light with a test light connected to battery voltage. Does test light illuminate? If yes, go to step  18. If no, go to next step.
  12. Probe battery voltage circuit of fuel injectors at fuel injector relay, with a test light connected to battery voltage. Does test light illuminate? If yes, go to step  19. If no, go to step  21.
  13. Probe ground circuit of both fuel injector relays with a test light connected to battery voltage. Does test light illuminate for both circuits? If yes, go to next step. If no, go to step  20.
  14. Turn OFF the ignition. Install both fuel injector relays. Disconnect a harness connector of a fuel injector from each bank of engine. Turn ON the ignition, with the engine OFF. Probe battery voltage circuit of fuel injectors with a test light connected to a known good ground. Does test light illuminate for both circuits? If yes, go to DIAGNOSTIC AIDS . If no, go to next step.
  15. Inspect for proper terminal contact at harness connector of appropriate fuel injector relay. Did you find and correct the condition? If yes, go to step  25. If no, go to step  22.
  16. Repair ignition voltage circuit of fuel injector relays for an open. After repairs, go to step  25.
  17. Repair ignition voltage circuit of fuel injector relays for a short to ground. After repairs, go to step  25.
    18. NOTE: Replace appropriate fusible link after short to ground is repaired.
  18. Repair short to ground in battery voltage circuit of fuel injector relay. After repairs, go to step  25.
    19. NOTE: Replace appropriate fusible link after short to ground is repaired.
  19. Repair short to ground in battery voltage circuit between fuel injector relay and fuel injectors. After repairs, go to step  25.
  20. Repair ground circuit of fuel injector relays for an open. After repairs, go to step  25.
  21. Repair battery voltage circuit of fuel injector relays for an open. After repairs, go to step  25.
  22. Replace appropriate fuel injector relay. After repairs, go to step  25.
  23. Replace AF fuel pump relay. After repairs, go to step  25.
  24. Replace AF ECM. After repairs, go to next step.
  25. Operate system in order to verify repair. Did you correct the condition? If yes, system is okay. If no, go to step  2.
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