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Home >> Buick >> 2003 >> Century Base >> Repair and Diagnosis >> Engine Performance >> System >> Engine Controls Self-Diagnostics - 3.1L Engine >> Diagnostic Tests >> DTC P0650: Mil Control Circuit >> Diagnostic Procedure
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Diagnostic Procedure

  1. Perform diagnostic system check - engine controls. See DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS  under SELF-DIAGNOSTIC SYSTEM. After performing diagnostic system check - engine controls, go to next step.
  2. Verify whether the instrument cluster is operational. If the Instrument Panel (IP) is completely inoperative, go to Instrument Cluster Diagnostic System Check in appropriate INSTRUMENT PANELS article in ACCESSORIES & EQUIPMENT. Command the MIL ON and OFF using a scan tool. Does the MIL turn ON and OFF when commanded using a scan tool? If yes, go to next step. If no, go to step  4.
  3. Observe the Freeze Frame/Failure Records for this DTC. Turn ignition switch to OFF position for 30 seconds. Start the engine. Operate the vehicle within the Conditions For Running Test. See CONDITIONS FOR RUNNING TEST . You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records. Does the DTC fail this ignition? If yes, go to next step. If no, go to INTERMITTENTS in TROUBLE SHOOTING - 3.1L CENTURY, GRAND PRIX & MALIBU article.
  4. Check the fuse that supplies battery voltage to the MIL. Is the fuse open? If yes, go to step  12. If no, go to next step.
  5. Turn ignition switch to OFF position. Disconnect the Powertrain Control Module (PCM) harness connectors. Turn ignition switch to RUN position. Is the MIL OFF? If yes, go to next step. If no, go to step  13.
  6. Turn ignition switch to OFF position. Remove the fuse that supplies voltage to the MIL. Turn ignition switch to RUN position, engine OFF. Measure the voltage from the MIL control circuit in the PCM to a good ground. Is the voltage less than 0.3 volt? If yes, go to next step. If no, go to step  14.
  7. Turn ignition switch to OFF position. Install the fuse that supplies voltage to the MIL. Turn ignition switch to RUN position, engine OFF. Connect a 3-amp fused jumper wire between the MIL control circuit of the PCM and a good ground. Is the MIL illuminated? If yes, go to step  11. If no, go to next step.
  8. Turn ignition switch to OFF position. Remove the Instrument Panel Cluster (IPC). Probe the MIL battery positive voltage circuit of the IPC harness connector using a test light connected to a good ground. Does the test light illuminate? If yes, go to next step. If no, go to step  15.
  9. Test the MIL control circuit for an open or high resistance. Did you find and correct a condition? If yes, go to step  18. If no, go to next step.
  10. Test for an intermittent and for a poor connection at the IPC. Did you find and correct the condition? If yes, go to step  18. If no, go to step  16.
  11. Test for an intermittent and for a poor connection at the PCM. Did you find and correct the condition? If yes, go to step  18. If no, go to step  17.
  12. Repair the short to ground in the battery positive voltage circuit. After repair, go to step  18.
  13. Repair the short to ground in the MIL control circuit. After repair, go to step  18.
  14. Repair the short to voltage in the MIL control circuit. After repair, go to step  18.
  15. Repair the open in the MIL battery positive voltage. After repair, go to step  18.
  16. Replace the IPC. After repair, go to step  18.
  17. Replace PCM. See POWERTRAIN CONTROL MODULE in appropriate REMOVAL & INSTALLATION article. Perform PCM relearn procedure. See POWERTRAIN CONTROL MODULE  under PROGRAMMING. After replacing PCM, go to next step.
  18. Using scan tool, clear DTCs. Turn ignition switch to OFF position for 30 seconds. Start the engine. Operate vehicle within the Conditions For Running Test. See CONDITIONS FOR RUNNING TEST . You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records. Did the DTC fail this ignition? If yes, go to step  2. If no, go to next step.
  19. Using the scan tool, observe the stored information in CAPTURE INFO. Does the scan tool display any DTCs that you have not diagnosed? If yes, see DIAGNOSTIC TROUBLE CODE DEFINITIONS . If no, system is okay at this time.
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