LEMON Manuals: Even more car manuals for everyone
Home >> GMC >> 1997 >> Forward Control 4.3 W, L35, Automatic >> Repair and Diagnosis >> External Pages >> Different variant/trim >> Section 10 (Engine Controls - Tests W/Codes - 6.5L Diesel (P Series)) >> Diagnostic Trouble Codes >> DTC P1641 - Malfunction Indicator Light (Mil) Control Circuit >> Diagnostic Procedures

Diagnostic Procedures

WARNING: This page is about a different variant/trim than selected.
  1. Perform Powertrain ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK. See the BASIC TESTING article. Then go to next step.
  2. Install scan tool. Turn ignition on, with engine off. Turn MIL on and off using scan tool. If MIL illuminates, go to next step. If MIL does not illuminate, go to step 4).
  3. DTC is intermittent. If other DTC(s) exist, go to that DTC for diagnosis. If no other DTC(s) exist, see DIAGNOSTIC AIDS.
  4. Turn ignition off. Disconnect PCM harness connector. Turn ignition on, with engine off. If MIL illuminates, go to next step. If MIL does not illuminate, go to step 7).
  5. Ignition on, engine off. Using a fused jumper wire, jumper PCM connector MIL driver circuit terminal to ground. If MIL illuminates, go to next step. If MIL does not illuminate, go to step 8).
  6. Check for poor connections at PCM. If problem was found, 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. Repair as necessary. After repairs, go to step 10).
  8. Check for the following conditions in MIL control circuit:
    • Open ignition feed.
    • Poor connections at PCM.
    • Faulty bulb.
    • Control circuit open or shorted to battery voltage.

    After repairs, go to step 10).

  9. Replace PCM. After replacing PCM, go to next step.
  10. Using scan tool, select DTC, CLEAR INFO. Start and warm engine to normal operating temperature. Select DTC, SPECIFIC, 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, repeat step 2).
  11. Using scan tool, select CAPTURE INFO, REVIEW INFO. If any undiagnosed DTC(s) are displayed, go to applicable DTC test.
scientia non olet · About LEMON Manuals