Fog/Driving Lamp Relay: Description and Operation

The fog lamp switch is a direct input to the BCM. The BCM sends a BUS message to the FCM informing it to turn ON the fog lamp relay. The fog lamp relay is then powered through low side control on pin 33 of the FCM. This circuit is electronically controlled and continuously monitored for malfunctions. Fog lamp functionality is not equipped on all vehicles. The FCM "learns" that the vehicle is equipped with fog lamps by reading the BCM BUS message.