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 Indicator Supply Voltage Circuit | 1 | 1 | -- | --
Fog Lamp Switch | 1 | 1 | 2 | --
1. Fog Lamp Indicator Inoperative 2. Fog Lamp Indicator Always ON

### 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 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 indicator supply voltage is supplied by the fog lamp relay coil circuit which also supplies voltage to the BCM for the fog lamp relay control circuit.

### 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, observe the scan tool fog lamp switch parameter while turning on the fog lamp switch. The reading should change between OFF and ON.

### Circuit/System Testing

1. Ignition OFF, disconnect the harness connector at the fog lamp switch.
2. Ignition OFF, test for less than 1 ohm of resistance between the ground circuit and ground.

⇒ | If greater than 1 ohm, test the ground circuit for an open/high resistance.

3. Verify the scan tool fog lamp switch parameter is OFF.

⇒ | If the fog lamp switch parameter is not indicating OFF, test the signal circuit for a short to ground.

4. Install a 3-amp fused jumper wire between the signal circuit and ground. Verify the scan tool fog lamp switch parameter is ON.

⇒ | If the fog lamp switch parameter is not indicating ON, test the signal circuit of the fog lamp switch for a short to voltage or an open/high resistance.

5. If all circuits test normal, test or replace the fog lamp switch.

### Component Testing

1. Ignition OFF, disconnect the harness connector at the fog lamp switch.
2. Test for infinite resistance between the signal terminal and the voltage supply terminal with the switch in the open position.

⇒ | If less than infinite resistance, replace the fog lamp switch.

3. Test for less than 2 ohms between the signal terminal and the voltage supply terminal with the switch in the closed position.

⇒ | If greater than 2.1 ohms, replace the fog lamp switch.

### Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

Fog Lamp Switch Replacement