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Home >> Chevrolet >> 1997 >> C3500 HD 7.4 J, Automatic >> Repair and Diagnosis >> External Pages >> Different variant/trim >> Section 3 (Engine Controls - Tests W/Codes - 6.5L) >> Diagnostic Trouble Codes >> DTC P1643 - Wait To Start Light 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 - 6.5L DIESEL article. Then go to next step.
  2. Turn ignition on, with engine off. Using scan tool, command glow plug system on. If WAIT TO START light illuminates, go to next step. If WAIT TO START light does not illuminate, go to step 4).
  3. DTC is intermittent. If no additional DTCs are set, see DIAGNOSTIC AIDS. If any additional DTCs are set, go to applicable DTC test.
  4. Turn ignition off. Disconnect PCM harness connector containing the WAIT TO START light control circuit. Turn ignition on, with engine off. If WAIT TO START light illuminates, go to step 7). If WAIT TO START light does not illuminate, go to next step.
  5. Using a fused jumper wire connected to ground, probe light control circuit in PCM harness connector. If WAIT TO START light illuminates, go to next step. If WAIT TO START light does not illuminate, go to step 8).
  6. Check connections at PCM. Repair as necessary. After repairs, go to step 10). If connections are okay, go to step 9).
  7. Check for short in WAIT TO START control circuit. Repair as necessary. After repairs, go to step 10).
  8. Check WAIT TO START circuit for open ignition feed to bulb, faulty bulb or control circuit that is open or shorted to voltage. Repair as necessary. 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.
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