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Home >> Buick >> 2003 >> Century Base >> Repair and Diagnosis >> Engine Performance >> System >> Engine Controls Self-Diagnostics - 3.1L Engine >> System Tests >> Mil Always On >> 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. Turn ignition switch to OFF position. Disconnect PCM harness connectors. Turn ignition switch to RUN position, engine off. Observe the MIL. Is the MIL illuminated? If yes, go to next step. If no, go to step  5.
  3. Check the MIL control circuit for a short to ground. Did you find and correct the condition? If yes, go to step  6. If no, go to next step.
  4. Replace IPC. Go to appropriate INSTRUMENT PANEL article in ACCESSORIES & EQUIPMENT. After replacing IPC, go to step  6.
  5. Replace PCM. See appropriate REMOVAL & INSTALLATION article. Perform PCM relearn procedure. See POWERTRAIN CONTROL MODULE  under PROGRAMMING. After repair, go to next step.
  6. Turn ignition switch to OFF position for 30 seconds. Start the engine. Does the vehicle operate correctly without any unwanted MIL illumination, and without any stored DTCs? If yes, system is okay at this time. If no, go to DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS .
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