For 1990-2009 cars

### 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 provide an overview of each diagnostic category.

### Circuit/System Description

Ignition voltage is supplied directly to the malfunction indicator lamp (MIL). The engine control module (ECM) turns the MIL ON by grounding the MIL control circuit. There should be a steady MIL with the ignition ON and the engine OFF.

### Reference Information

#### Schematic Reference

Engine Controls 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 Control Module References for scan tool information

### Circuit/System Verification

1. Ignition ON, engine OFF, observe the transmission DTC information with a scan tool. There should be no transmission DTCs set.

⇒ | If a DTC is set, refer to Diagnostic Trouble Code (DTC) List - Vehicle.

2. Command the MIL ON and OFF with a scan tool. The MIL should turn ON and OFF when commanded.
3. Engine idling, 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. If any other indicators are inoperative, refer to Symptoms - Displays and Gages.
2. Ignition OFF, disconnect the ECM harness connector X1.
3. Ignition ON, the MIL should not illuminate.

⇒ | If the MIL illuminates, test the MIL control circuit terminal 1-X1 for a short to ground. If the circuit test normal, replace the bulb/IPC.

4. Ignition ON, connect a 3 A fused jumper wire between the MIL control circuit terminal 1-X1 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 test normal, replace the bulb/IPC.

5. If all circuits test normal, replace the ECM.

### Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

• | Instrument Cluster Bulb Replacement

• | Control Module References for ECM replacement, setup, and programming