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
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 (except L96) [1][2]Electrical DiagramsEngine Controls Schematics (L96) [1][2]Electrical Diagrams
* Instrument Cluster Schematics Instrument Cluster Schematics
Connector End View Reference
Component Connector End Views 1-2 Shift Solenoid (SS) Valve (M30)
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. 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 display OK or Not Run.
3. Engine running, 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 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 circuit terminal 52-X1 with L96
* ECM circuit terminal 68-X1 without L96
3. Connect a 3 A fused jumper wire between the MIL control circuit terminal listed below and ground. The MIL should illuminate.
* ECM circuit terminal 52-X1 with L96
* ECM circuit terminal 68-X1 without L96
• If the MIL illuminates, replace the ECM.
• If the MIL does not illuminate, test the MIL control circuit for a short to voltage, or an open/high resistance. If the MIL control circuit tests normal, test the instrument cluster ignition voltage circuit for a short to ground or open/high resistance. If the circuit tests normal, replace the instrument cluster/bulb.
Repair Instructions
Perform the Diagnostic Repair Verification Verification Tests after completing the diagnostic procedure.
* Instrument Cluster Replacement (With RPO SLT) Instrument Cluster Replacement (With RPO SLT)Instrument Cluster Replacement (Without RPO SLT) Instrument Cluster Replacement (Without RPO SLT)
* Control Module References Control Module References for ECM replacement, setup, and programming