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Home >> GMC >> 2000 >> C3500 HD 6.5 F, Automatic >> Repair and Diagnosis >> Engine Performance >> System >> Engine Control System Self-Diagnostics - Diesel >> Diagnostic Tests >> DTC P1641: Malfunction Indicator Light Control Circuit >> Diagnostic Procedures

Diagnostic Procedures

  1. If OBD system check has been performed, go to next step. If OBD system check has not been performed, see ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK  under SELF-DIAGNOSTIC SYSTEM.
  2. Connect scan tool. Start and idle engine. Using scan tool, command MIL on and off. If MIL illuminates, go to next step. If MIL does not illuminate, go to step  4.
  3. DTC is intermittent. If other DTCs are set, perform appropriate DTC test. If no other DTCs are set, see DIAGNOSTIC AIDS .
  4. Turn ignition off. Disconnect 32-pin PCM harness connector (Blue). Turn ignition on. If MIL does not illuminate, go to next step. If MIL illuminates, go to step  7.
  5. Turn ignition on. Connect fused jumper wire between ground and MIL control circuit at PCM harness connector. If MIL illuminates, go to next step. If MIL does not illuminate, go to step  8.
  6. Check for poor connections at PCM. Repair as necessary. After repairs, go to step  10. If connections are okay, go to step  9.
  7. Repair short to ground in MIL control circuit. After repairs, go to step  10.
  8. Check MIL control circuit for open ignition feed circuit, faulty bulb, or open or short to battery voltage. Repair as necessary. After repairs, go to step  10.
  9. Replace PCM. Perform PCM relearn procedures. See PROGRAMMING . After repairs, go to next step.
  10. Using scan tool, clear DTCs. Start and warm engine to normal operating temperature. Select DTC, SPECIFIC, and then enter DTC P1641. Operate vehicle within the conditions for setting this DTC. If scan tool indicates that this test ran and passed, go to next step. If scan tool does not indicate that this test ran and passed, go to step  2.
  11. Using scan tool, check for DTCs. If any undiagnosed DTCs are set, perform appropriate DTC test. If no DTCs are set, system is okay.
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