GM/Detroit 6.5L ENGINE CONTROLS – No Malfunction Indicator Lamp

Circuit Description
There shoul d always be a steady malfunction indicator lamp (MIL) when the ignition is ON and the engine is OFF. Battery ignition voltage is supplied to the lamp.
The PCM will turn the lamp ON by grounding the ignition feed circuit.

Diagnostic Aids
If the engine cranks but will not run, check:
• Continuous battery-fuse or fusible link for open.
• PCM ignition fuse for open.
• Battery Feed circuit to PCM for open.
• Ignition Feed circuit to PCM for open.
• Poor connection to PCM.

An intermittent may be caused by any of the following conditions:
• A poor connection
• Rubbed through wire insulation
• A broken wire inside the insulation

Thoroughly check any circuitry that is suspected of causing the interm ittent com plaint. Refer to Intermittents and Poor Connections Diagnosis in Wiring Systems.

If a repair is necessary, then refer to W iring Repairs or Connector Repairs in W iring Systems.

Test Description
Number(s) below refer to the step number(s) on the Diagnostic Table.
5. This step will isolate the problem in the MIL control circuit.
6. If the Battery Feed, Ignition Feed and Diagnostic Test circuits have voltage, the PCM connections,
grounds, or PCM are malfunctioning.
8. Refer to PCM Connector End Views fo r PCM pin locations of ground circuits.
12. If the fuse/fusible link is open, refer to PCM Wiring Diagram for complete circuit.


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