Exterior Lighting System

EXTERIOR LIGHTING SYSTEM

HEADLAMP POWER
The Headlamp Switch is a direct input to the BCM. The BCM sends a BUS message to the FCM informing it of a headlamp switch status change. The FCM then turns on power to the headlamps through four "fuseless" circuits. These circuits are electronically controlled and continuously monitored for malfunctions. Power is supplied to each filament in a separate circuit. For vehicles equipped with daytime running Lamps (DRL), the FCM electronically steps down the headlamp voltage to provide the desired illumination.

HEADLAMP SWITCH
The Headlamp Switch uses a multiplexed (MUX) circuit to the Body Control Module (BCM). The Headlamp Switch controls the Fog lamp relay, Park lamps and the Low and High headlamps. The BCM then sends a signal through the PCI Bus line to the FCM as to what state the switch has selected. The FCM energizes the high side output drivers to turn ON the desired lamps.

PARK LAMP RELAY
The Park Lamp Switch is a direct input to the BCM. The BCM sends a BUS message to the FCM informing it to turn on the park lamp relay. The park lamp relay is then powered through low side control of the FCM. This circuit is electronically controlled and continuously monitored for malfunctions.

FOG LAMP RELAY
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 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.

FOG LAMPS
The BCM controls the operation of the fog lamp relay that turns the fog lamps ON and OFF. The Fog lamps can only be ON when the park and low beams are ON. If the high beams are switched ON then the Fog lamps will be automatically turned OFF.

EXTERIOR LIGHTING BATTERY SAVER
The BCM monitors the status of, and controls, the Park Lamps, Headlamps and Fog Lamp relays. If any exterior lamps are left ON after the ignition is turned OFF, the BCM will turn them OFF after 3 minutes.

AUTO HEADLAMPS
This feature is available on vehicles equipped with both the Electrocromatic Mirror (ECM) and the Compass/Mini-Trip Computer (CMTC). When the BCM detects a day/night signal from the CMTC, an ECM is present and Auto Headlamp mode is selected.