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Diagnostic Procedure

WARNING: This page is about a different car, the 2003 Cadillac Seville and 2003 Cadillac DeVille. However, it is still accessible from the selected car via links, so may be relevant.
  1. If diagnostic system check has already been performed, go to next step. If diagnostic system check has not been performed, go to DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS - 4.6L DEVILLE & SEVILLE article.
  2. Connect scan tool. Turn ignition ON, with the Engine OFF. Using scan tool, command fuel pump relay ON and OFF. If fuel pump turns ON and OFF, check for intermittent problem. See INTERMITTENT CONDITIONS under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS - 4.6L DEVILLE & SEVILLE article. If fuel pump does not turn ON and OFF, go to next step.
  3. Using scan tool, command fuel pump relay ON and OFF. If fuel pump relay clicks, go to step  9. If fuel pump relay does not click, go to next step.
  4. Turn ignition OFF. Disconnect fuel pump relay located in rear fuse block under rear seat cushion. See Figure. Turn ignition ON. Using test light connected to ground, probe fuel pump relay control circuit at relay cavity. Using scan tool, command fuel pump relay ON and OFF. If test light turns on and OFF, go to next step. If test light does not turn on and off, go to step  6.
  5. Connect test light between fuel pump relay control circuit and fuel pump relay ground circuit at relay cavities. Using scan tool, command fuel pump relay ON and OFF. If test light turns on and off, go to step  21. If test light does not turn on and off, go to step  24.
  6. If test light remains illuminated with each command, go to next step. If test light does not illuminate at all, go to step  8.
  7. Disconnect PCM. PCM is located on left side of engine compartment, inside air filter assembly. Check for short to voltage in fuel pump relay control circuit. Repair as necessary. After repairs, go to step  29. If circuit is okay, go to step  28.
  8. Disconnect PCM. PCM is located on left side of engine compartment, inside air filter assembly. Check for open or short to ground in fuel pump relay control circuit. Repair as necessary. After repairs, go to step  29. If circuit is okay, go to step  22.
  9. Turn ignition ON. If fuel pump runs continuously, go to next step. If fuel pump does not run continuously, go to step  11.
  10. Turn ignition OFF. Disconnect fuel pump relay located in rear fuse block under rear seat cushion. See Figure. Turn ignition ON. If fuel pump runs continuously, go to step  23. If fuel pump does not run continuously, go to step  27.
  11. Check F/PMP fuse (20-amp) located in rear fuse block under rear seat cushion. See Figure. If fuse is open, go to next step. If fuse is okay, go to step  14.
  12. Disconnect fuel pump harness in-line connector located near fuel tank. See Figure. Test supply voltage circuit of fuel pump for a grounded circuit. See Figure. Repair as necessary. After repairs, go to step  29. If fuel pump harness in-line connector is okay, go to next step.
  13. Lower fuel tank if necessary. Test or inspect the fuel tank electrical harness for damage to the harness or a grounded circuit. Repair as necessary. Replace the fuel pump fuse if necessary. After repairs, go to step  29. If fuel tank harness is okay, go to step  20.
  14. Turn ignition OFF. Disconnect fuel pump relay located in rear fuse block under rear seat cushion. See Figure. Turn ignition ON. Using test light connected to ground, probe fuel pump relay battery feed circuit at relay cavity. If test light illuminates, go to next step. If test light does not illuminate, go to step  25.
  15. Connect fused jumper wire between fuel pump relay battery feed circuit and fuel pump power feed circuit at relay cavities. If fuel pump runs, go to step  21. If fuel pump does not run, go to next step.
  16. Remove fuel pump access panel. Check for open or high resistance in fuel pump power feed circuit between fuel pump relay and fuel pump. See Figure. Repair as necessary. After repairs, go to step  29. If circuit is okay, go to next step.
    17. NOTE: Inspect the ground circuit for being tight, corrosion on terminals, or damage to wiring harness.
  17. Test ground circuit of fuel pump for an open or high resistance between body pass through connector and ground. Repair as necessary. After repairs, go to step  29. If circuit is okay, go to next step.
  18. Test for an intermittent and a poor connection at the fuel pump in-line connector to the body pass through connector. Repair as necessary. After repairs, go to step  29. If connector is okay, go to next step.
  19. Lower the fuel tank. Refer to FUEL TANK under FUEL SYSTEMS in REMOVAL & INSTALLATION - DEVILLE & SEVILLE article. Test or inspect the fuel tank electrical harness for damage to the harness or an open circuit. Repair as necessary. After repairs, go to step  29. If harness and circuit are okay, go to go to step  26.
  20. Reconnect all components. Install NEW F/PMP fuse. Using scan tool, command fuel pump relay ON. If fuse blows, go to step  26. If fuse does not blow, check for intermittent problem. See INTERMITTENT CONDITIONS under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS - 4.6L DEVILLE & SEVILLE article.
  21. Check for poor connections at fuel pump relay. Repair as necessary. After repairs, go to step  29. If connections are okay, go to step  27.
  22. Check for poor PCM harness connections. Repair as necessary. After repairs, go to step  29. If connections are okay, go to step  28.
  23. Repair short to voltage in fuel pump power feed circuit. After repairs, go to step  29.
  24. Repair open in fuel pump relay ground circuit. After repairs, go to step  29.
  25. Repair open in fuel pump relay battery feed circuit. After repairs, go to step  29.
  26. Replace fuel pump. See FUEL PUMP under FUEL SYSTEMS in REMOVAL & INSTALLATION - DEVILLE & SEVILLE article. After repairs, go to step  29.
  27. Replace fuel pump relay. After repairs, go to step  29.
  28. Replace PCM. See POWERTRAIN CONTROL MODULE under COMPUTERIZED ENGINE CONTROLS in REMOVAL & INSTALLATION - DEVILLE & SEVILLE article. After repairs, go to next step.
  29. Operate system to verify repair. If system operation is okay, testing is complete. If system operation is not okay, go to step  2.
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