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.

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:

Schematic Reference

Fog Lights Schematics

Connector End View Reference

Lighting Systems Connector End Views

Electrical Information Reference

Scan Tool Reference

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.

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.

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.