Malfunction Indicator Lamp: Testing and Inspection

Malfunction Indicator Lamp (MIL) Diagnosis

Diagnostic Instructions

- Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure.
- Review Strategy Based Diagnosis for an overview of the diagnostic approach.
- Diagnostic Procedure Instructions provides an overview of each diagnostic category.

Circuit/System Description

The malfunction indicator lamp (MIL) illuminates to inform the driver that an emission system fault has occurred and the engine control system requires service. Ignition voltage is supplied directly to the MIL and, when the emission system fault occurs, the engine control module (ECM) turns the MIL ON by grounding the MIL control circuit. Under normal operating conditions, the MIL should be ON only when the ignition is ON and the engine is OFF.

Diagnostic Aids

If the condition is intermittent, move the related harnesses and connectors with the ignition ON and the engine OFF, and with the engine operating while monitoring the scan tool MIL control circuit status parameters. The MIL control circuit status parameters will change from OK or Not Run to Fault if there is a condition with the circuit or a connection.

Reference Information

Schematic Reference

- Engine Controls Schematics (3.0L (LF1)) Engine Controls Schematics (2.8L (LAU))
- Instrument Cluster Schematics

Connector End View Reference
Component Connector End Views

Electrical Information Reference

- Circuit Testing
- Connector Repairs
- Testing for Intermittent Conditions and Poor Connections
- Wiring Repairs

Scan Tool Reference
Control Module References for scan tool information

Circuit/System Verification

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:
- The MIL Control Circuit Low Voltage Test Status
- The MIL Control Circuit Open Test Status
- The MIL Control Circuit High Voltage Test Status

Each parameter should display OK or Not Run.

3. Operate the vehicle within the Conditions for Running the DTC to verify the DTC does not reset. You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records data.

Circuit/System Testing

1. Ignition OFF, disconnect the harness connector listed below at the K20 ECM.
- ECM harness connector X2 with LAU
- ECM harness connector X1 with LF1

2. Ignition ON, the MIL should not illuminate.
3. If the MIL is illuminated, test the MIL control circuit listed below for a short to ground. If the circuit tests normal, replace the P16 instrument cluster.
- ECM circuit terminal 12 X2 with LAU
- ECM circuit terminal 46 X1 with LF1

4. Connect a 3 A fused jumper wire between the MIL control circuit listed below and ground. The MIL should illuminate.
- ECM circuit terminal 12 X2 with LAU
- ECM circuit terminal 46 X1 with LF1

5. If the MIL illuminates, replace the K20 ECM.
6. 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, test the instrument cluster ignition voltage circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the P16 instrument panel cluster/bulb.

Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

- Control Module References for ECM replacement, setup, and programming.
- Instrument Cluster Replacement