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Home >> GMC >> 2003 >> Jimmy 4D Utility, 4WD, Part Time >> Repair and Diagnosis >> Engine Performance >> System >> Engine Controls - System & Component Testing - 4.3L >> Fuel Systems >> Fuel Pump Electrical Circuit Diagnosis >> Diagnostic Procedures

Diagnostic Procedures

  1. Perform diagnostic system check. See DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS under SELF DIAGNOSTIC SYSTEM in SELF DIAGNOSTICS - 4.3L ASTRO, BLAZER, JIMMY CANADIAN, SAFARI, SONOMA & S10 PICKUP article. After performing diagnostic system check, go to next step.
  2. Turn ignition on, with engine off. Using scan tool, command fuel pump relay on and off. Repeat commands as necessary. Does fuel pump turn on and off? If yes, problem is intermittent. If no, go to next step.
  3. Using scan tool, command fuel pump relay on and off. Fuel pump relay is located in underhood fuse/relay block. See Figure. Do you hear a click when you command fuel pump relay on and off? If yes, go to step  9. If no, go to next step.
  4. Turn ignition off. Remove fuel pump relay. Turn ignition on, with engine off. Probe control circuit of fuel pump relay with a test light that is connected to a good ground. See Figure. Command fuel pump relay ON and OFF with a scan tool. Does test light turn ON and OFF? If yes, go to next step. If no, go to step  6.
  5. Connect a test light between control circuit of fuel pump relay and ground circuit of fuel pump relay. Command fuel pump relay on and off with a scan tool. Does test light turn on and off? If yes, go to step  19. If no, go to step  22.
  6. Does test light remain illuminated with each command? If yes, go to next step. If no, go to step  8.
  7. Test control circuit of fuel pump relay for a short to voltage. See Figure. Did you find and correct condition? If yes, go to step  27. If no, go to step  26.
  8. Test control circuit of fuel pump relay for a short to ground or an open. Did you find and correct condition? If yes, go to step  27. If no, go to step  20.
  9. Turn ignition on, with engine off. Does fuel pump operate continuously? If yes, go to next step. If no, go to step  11.
  10. Turn ignition off. Remove fuel pump relay. Turn ignition on, with engine off. Does fuel pump operate continuously? If yes, go to step  21. If no, go to step  25.
  11. Inspect fuel pump fuse. Is fuse open? If yes, go to next step. If no, go to step  14.
  12. Test supply voltage circuit of fuel pump for a short to ground between fuel pump fuse and fuel pump. Replace fuel pump fuse, if necessary. Did you find and correct condition? If yes, go to step  27. If no, go to next step.
  13. Connect all disconnected electrical components. Install a new fuel pump fuse. Command fuel pump relay on with a scan tool. Inspect fuel pump fuse. Is fuse open? If yes, go to step  24. If no, problem is intermittent.
  14. Turn ignition off. Remove fuel pump relay. Turn ignition on, with engine off. Probe ignition 1 voltage circuit of fuel pump relay, switch side, 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. Connect a 20-amp fused jumper wire between ignition 1 voltage circuit of fuel pump relay and supply voltage circuit of fuel pump. Does fuel pump operate? If yes, go to step  19. If no, go to next step.
  16. Test supply voltage circuit of fuel pump for an open or high resistance between fuel pump relay and fuel pump. Did you find and correct condition? If yes, go to step  27. If no, go to next step.
  17. Test ground circuit of fuel pump for an open or high resistance. Did you find and correct condition? If yes, go to step  27. If no, go to next step.
  18. Test for an intermittent and for a poor connection at fuel sender cover. Did you find and correct condition? If yes, go to step  27. If no, go to step  24.
  19. Test for an intermittent and for a poor connection at fuel pump relay. Did you find and correct condition? If yes, go to step  27. If no, go to step  25.
  20. Test for an intermittent and for a poor connection at PCM. Did you find and correct condition? If yes, go to step  27. If no, go to step  26.
  21. Repair short to voltage in supply voltage circuit of fuel pump. After repairs, go to step  27.
  22. Repair open or high resistance in ground circuit of fuel pump relay. After repairs, go to step  27.
  23. Repair open in ignition 1 voltage circuit of fuel pump relay. After repairs, go to step  27.
  24. Inspect for poor connections at fuel pump, within fuel tank, before replacing fuel pump. Replace fuel sender. Replace fuel pump fuse, if necessary. After repairs, go to step  27.
  25. Replace fuel pump. After replacing fuel pump, go to step  27.
  26. Replace PCM. See REMOVAL & INSTALLATION - ASTRO & SAFARI or REMOVAL & INSTALLATION - BLAZER, JIMMY CANADIAN, SONOMA & S10 PICKUP article. Perform PCM programing. After replacing PCM, go to next step.
  27. Operate system in order to verify repair. Did you correct condition? If yes, system is okay. If no, go to step  2.
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