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.

### Diagnostic Fault Information

Circuit | Short to Ground | Open/High Resistance | Short to Voltage | Signal Performance
--- | --- | --- | --- | ---
Fog Lamp Bulb Signal Circuit | 2 | 2 | 1 | --
Fog Lamp Bulb Ground Circuit | -- | 2 | 2 | --
Fog Lamp Switch Signal Circuit | 1 | 2 | 2 | --
Fog Lamp Switch Ground Circuit | -- | 2 | 2 | --
1. Fog Lamps Always ON 2. Fog Lamps Inoperative

### Circuit/System Description

The fog lamp fuse in the fuse block - underhood supplies battery positive voltage to the switch side of the fog lamp relay at all time. When the fog lamp switch is pressed it supplies a momentary voltage signal on the front fog lamp switch signal circuit to the body control module (BCM). The BCM then supplies ground to the coil side of the fog lamp relay energizing the relay. The fog lamp relay is soldered to the underhood fuseblock circuit board. The front fog lamps are connected to ground at G101. The park lamps or headlamps must be ON for the fog lamps to operate.

### Diagnostic Aids

The fog lamp relay is soldered to the underhood fuseblock. In order to replace the fog lamp relay the replacement of the underhood fuseblock must also be done.

A short to voltage, a short ground or an open in the following locations may cause a malfunction to occur:

• | The control circuit of the fog lamps relay.

• | The fog lamps relay.

• | The BCM

### Reference Information

#### Schematic Reference

Fog Lights Schematics

#### Connector End View Reference

Lighting Systems 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 Definitions

• | Scan Tool Data List

• | Scan Tool Output Controls

### Circuit/System Verification

Ignition ON, turn the fog lamp switch ON and OFF, observe the fog lamp relay display. The fog lamp relay should turn ON and OFF with each command.

### Circuit/System Testing

#### Fog Lamp Relay, BCM, and Underhood Fuseblock Circuit Testing

1. Ignition OFF, disconnect the fog lamp relay, underhood fuseblock terminal C2 pin19.
2. Ignition ON, verify the fog lamps are deactivated.

⇒ | If the fog lamps are still activated, repair the relay switch control circuit for a short to voltage.

3. Connect a 10-amp fused jumper wire between the underhood fuseblock B+ circuit and the fog lamp signal circuit, BCM terminal C3 pin21. Verify the fog lamps are activated.

⇒ | If the fog lamps are not activated, test the fog lamp signal circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the underhood fuse block.

4. Connect a test lamp between the relay coil control circuit terminal C4 pin11 and the underhood fuseblock B+ circuit.
5. Turn the fog lamp relay ON and OFF by turning ON and OFF the fog lamp switch. The test lamp should turn ON and OFF when changing between the commanded states.

⇒ | If the test lamp remains ON all the time, test for a short to ground on the relay coil control circuit. If the circuit tests normal, replace the BCM.

⇒ | If the test lamp remains OFF all the time, test for a short to voltage or an open/high resistance on the relay coil control circuit. If the circuit tests normal, replace the BCM.

6. If all circuits test normal, test or replace the underhood fuseblock.

### Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

• | Control Module References for BCM replacement, setup, and programming.

• | Underhood Electrical Center or Junction Block Replacement