Important: Always perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure.

Ignition voltage is supplied to the malfunction indicator lamp (MIL). The engine control module (ECM) turns the MIL ON by grounding the MIL control circuit.

Schematic Reference

Connector End View Reference

Electrical Information Reference

Scan Tool Reference

The MIL should turn ON and OFF when commanded with a scan tool.

1. Turn OFF the ignition.
2. Disconnect the ECM.
3. Turn ON the ignition with the engine OFF.

⇒	If the MIL is still ON, test the MIL control circuit for a short to ground.

⇒	If the MIL control circuit tested OK and the MIL stayed ON, replace the instrument panel cluster (IPC).

⇒	If the MIL control circuit tested OK and the MIL went out when the ECM was disconnected, replace the ECM.

4. Measure for 12 volts from the MIL ignition voltage circuit in the ECM harness connector to a ground.

⇒	If there is less than 12 volts, test the MIL ignition voltage circuit for an open, or a short to ground and an open fuse.

5. Remove the fuse that supplies voltage to the MIL.
6. Measure for less than one volt from the MIL control circuit in the ECM harness connector to a good ground.

⇒	If there is more than one volt, test the MIL control circuit for a short to voltage.

7. Install the fuse that supplies voltage to the MIL.
8. The MIL should illuminate with a 3-amp fused jumper wire connected between the MIL control circuit in the ECM harness connector and a good ground.

⇒	If the MIL does not illuminate, test the MIL control circuit for an open or high resistance.

⇒	If the MIL control circuit tests OK, replace the IPC.

⇒	If the MIL does illuminate, but does not when commanded ON with a scan tool, replace the ECM.

Important: Always perform the Diagnostic Repair Verification after completing the diagnostic procedure.