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 front fog lamps are connected to ground at G101. The foglamp relay is soldered to the underhood fuseblock circuit board. 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 circuit board. 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 Circuit Testing

1. Ignition OFF, disconnect the fog lamp relay, underhood fuseblock terminal C2 pin19.
2. Ignition ON, verify that a test lamp illuminates between the underhood fuseblock B+ circuit and ground.

⇒ | If the test lamp does not illuminate, repair the voltage supply circuit for a short to ground or an open/high resistance. If the voltage supply circuit fuse is open, test the relay switch control circuit underhood fuseblock terminal C3 pin 4 for a short to ground. If the circuit tests normal, replace the underhood fuseblock.

3. Disconnect the harness connector at the fog lamp bulbs.
4. Test for less than 1 ohm of resistance between the fog lamp bulb ground circuit and ground

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

5. Connect the harness connector at the fog lamp bulbs.
6. Connect a 10-amp fused jumper wire between the relay switch voltage supply circuit and the fog lamp signal circuit. 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.

7. Connect a test lamp between the relay coil control circuit BCM terminal C4 pin 11 and the underhood fuseblock B+ circuit.
8. 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.

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

#### Fog Lamp Switch Circuit Testing

1. Ignition OFF, disconnect the harness connector at the fog lamp switch, pin 4.
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. If the circuit test normal, replace the BCM.

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

⇒ | If not inactive, test the signal circuit for a short to ground. If the circuit tests normal, replace the BCM.

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

⇒ | If not active, test the signal circuit of the fog lamp switch for a short to voltage or an open/high resistance. If circuit tests normal, replace the BCM.

5. If all circuits test normal, test or replace the head lamp switch located within the mutifunction switch.

#### Fog Lamp Switch Testing

1. Ignition OFF, disconnect the harness connector at the headlamp switch, pin 4.
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 headlamp switch located within the multifunction switch.

3. Test for less than 1.5 ohms between the signal terminal and the voltage supply terminal with the switch in the closed position.

⇒ | If greater than 1.5 ohms, replace the headlamp switch located within the multifunction switch.

### Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

• | Instrument Panel Lamp Dimmer Switch Replacement

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

• | Underhood Electrical Center or Junction Block Replacement

• | Turn Signal Multifunction Switch Replacement