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 voltage is supplied to the malfunction indicator lamp (MIL). The Engine Control Module (ECM) turns the MIL ON by applying a ground to the MIL control circuit.

### Reference Information

#### Schematic Reference

Engine Controls Schematics

#### Connector End View Reference

• | Engine Controls Connector End Views

• | Engine Control Module Connector End Views

#### Electrical Information Reference

• | Circuit Testing

• | Connector Repairs

• | Testing for Intermittent Conditions and Poor Connections

• | Wiring Repairs

#### Scan Tool Reference

• | Scan Tool Data List

• | Scan Tool Data Definitions

• | Scan Tool Output Controls

### Circuit/System Verification

Ignition ON, the MIL should turn ON and OFF when commanded with a scan tool.

### Circuit/System Testing

1. Ignition OFF, disconnect the harness connector at the instrument panel cluster (IPC).
2. Ignition ON, verify that the test lamp illuminates between the ignition circuit and ground.

⇒ | If the test lamp does not illuminate, test the ignition circuit for short or open to ground, or high resistance. If the circuit tests normal and the ignition circuit fuse is open, replace the IPC.

3. Connect a test lamp between the control circuit and the ignition circuit.
4. Command the MIL ON and OFF with a scan tool. The test lamp should turn ON and OFF when changing between the commanded states.

⇒ | If the test lamp remains illuminates, test the control circuit for a short to ground. If the circuit test normal, replace the ECM.

⇒ | If test lamp remains OFF, test the control circuit for a short to voltage, or an open or high resistance. If the circuit test normal, replace the ECM.

⇒ | If all circuits test normal, replace the IPC.

### Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

• | Instrument Cluster Replacement

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