The malfunction indicator lamp (MIL) is located on the instrument panel cluster (IPC). The MIL informs the driver that an emission system fault has occurred and that the engine control system requires service. The engine control module (ECM) monitors the MIL control circuit for conditions that are incorrect for the commanded state of the MIL. For example, a failure condition exists if the ECM detects low voltage when the MIL is commanded OFF, or high voltage when the MIL is commanded ON.

If the condition is intermittent, move the related harnesses and connectors with the engine operating. Monitor the scan tool Circuit Test Status parameters for the component. The Circuit Test Status parameter will change from OK or Not Run to Fault if there is a condition with the circuit or a connection.

Schematic Reference

Connector End View Reference

Component Connector End Views

Electrical Information Reference

Scan Tool Reference

Control Module References for scan tool information

1. Ignition ON, command the MIL ON and OFF with a scan tool. The MIL should turn ON and OFF as commanded.
2. Command the MIL ON and OFF with a scan tool while observing the following control circuit status parameters:

•	MIL Ckt. Short Gnd Test Status

•	MIL Ckt. Open Test Status

•	MIL Ckt. Short Volts Test Status

•	Each parameter should change between OK to Not run or from Not Run to OK.

1. Ignition ON, verify that the IPC warning indicators are illuminated.

⇒	If the IPC warning indicators are not illuminated, test the IPC ignition circuit for a short to ground or an open/high resistance. If the circuit tests normal and the ignition circuit fuse is open, replace the IPC.

2. Ignition OFF, disconnect the ECM X1 harness connector. Ignition ON, the MIL should not illuminate.

⇒	If the MIL is illuminated, test the MIL control circuit terminal X1-12 for a short to ground. If the circuit tests normal, replace the IPC.

3. Ignition ON, connect a 3A fused jumper wire between the MIL control circuit terminal X1-12 and ground. The MIL should illuminate.

⇒	If the MIL does not illuminate, test the MIL control circuit for a short to voltage, or an open/high resistance. If the circuit tests normal, replace the IPC/bulb.

4. If all circuits/connections test normal, replace the ECM.

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.