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 provides an overview of each diagnostic category.

### Circuit/System Description

Ignition 1 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.

### MIL Operation

The MIL is located on the instrument panel (I/P).

### MIL Function

• | The MIL informs the driver that a malfunction has occurred and the vehicle should be taken in for service as soon as possible.

• | The MIL illuminates during a bulb test and a system test.

• | A DTC will be stored if a MIL is requested by the diagnostic.

### MIL Illumination

• | The MIL will illuminate with the ignition switch ON and the engine not running.

• | The MIL will turn OFF when the engine is started.

• | The MIL will remain ON if the self-diagnostic system has detected a malfunction.

• | The MIL may turn OFF if the malfunction is no longer present.

• | If the MIL is illuminated and then the engine stalls, the MIL will remain illuminated as long as the ignition switch is ON.

• | If the MIL is not illuminated and the engine stalls, the MIL will not illuminate until the ignition switch is cycled OFF, then ON.

### 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 for scan tool information

### Circuit/System Testing

1. Ignition OFF, disconnect the harness connector at the ECM.
2. Ignition ON, observe the malfunction indicator lamp (MIL).

⇒ | If the MIL is illuminated, test the control circuit for a short to ground between the ECM and the I/P. If the circuit tests normal, replace the I/P or the DIC/clock.

⇒ | If the MIL is not illuminated, replace the ECM.

### Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

• | Instrument Panel Assembly Replacement

• | Clock Replacement

• | Control Module References for engine control module replacement, setup, and programming.