Malfunction Indicator Lamp (MIL) Diagnosis

Malfunction Indicator Lamp (MIL) Diagnosis

Diagnostic Instructions

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

Circuit/System Description

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.

Reference Information
Schematic Reference

* Instrument Cluster Schematics (Instrument Cluster Schematics)
* Engine Controls Schematics (except L96) ([1][2]Electrical Diagrams)Engine Controls Schematics (L96) ([1][2]Electrical Diagrams)

Connector End View Reference

Component Connector End Views (Connector End Views By Name)
Electrical Information Reference

* Circuit Testing (Circuit Testing)
* Connector Repairs (Connector Repairs)
* Testing for Intermittent Conditions and Poor Connections (Testing for Intermittent Conditions and Poor Connections)
* Wiring Repairs (Wiring Repairs)

Scan Tool Reference

Control Module References (Control Module References) for scan tool information

Circuit/System Verification

Note: Any MIL requesting DTCs that may be set should be diagnosed first.

1. Ignition ON, command the MIL ON and OFF with a scan tool. The MIL should turn ON and OFF as commanded.
2. Ignition ON, observe each of the MIL control circuit Test Status parameters listed below with a scan tool:

* MIL Ckt Short Gnd Test Status
* MIL Ckt Open Test Status
* MIL Ckt Short Volts Test Status
Each parameter should display OK or Not Run.

Circuit/System Testing

1. Ignition OFF, disconnect the X1 harness connector at the K20 ECM.
2. Ignition On, the MIL should not illuminate.

• If the MIL is illuminated, test the MIL control circuit terminal listed below for a short to ground. If the circuit tests normal, replace the instrument panel cluster.

* ECM terminal X1-52 for RPO L96
* ECM terminal X1-68 for all other RPOs

3. Connect a 3 A fused jumper wire between the MIL control circuit terminal listed below and ground. The MIL should illuminate.

* ECM terminal X1-52 for RPO L96
* ECM terminal X1-68 for all other RPOs

• If the MIL illuminates, replace the ECM.

• If the MIL does not illuminate, test the appropriate MIL control circuit for a short to voltage, or an open/high resistance. If the MIL control circuit tests OK, test the instrument panel cluster ignition circuit for a short to ground or open/high resistance. If the circuit tests normal, replace the instrument panel cluster/bulb.

Repair Instructions

Perform the Diagnostic Repair Verification (Verification Tests) after completing the diagnostic procedure.

* Instrument Cluster Replacement (Without RPO SLT) (Instrument Cluster Replacement (Without RPO SLT))Instrument Cluster Replacement (With RPO SLT) (Instrument Cluster Replacement (With RPO SLT))
* Control Module References (Control Module References) for ECM replacement, setup, and programming