Circuit/System Description

The body control module (BCM) monitors three signal circuits from the Turn Signal Switch. When the Turn Signal Switch is in the AUTO position, all three signal circuits are open. When placed in the AUTO position, the BCM monitors inputs from the ambient light sensor to determine if headlamps are required or if daytime running lamps will be activated based on outside lighting conditions. When the Turn Signal Switch is placed in the OFF position, the Turn Signal Switch headlamps OFF signal circuit is grounded momentarily, indicating to the BCM that the exterior lamps should be turned OFF. With the Turn Signal Switch in the PARK position, the Turn Signal Switch park lamps ON signal circuit is grounded, indicating that the park lamps have been requested. When the Turn Signal Switch is placed in the HEADLAMP position, both the Turn Signal Switch park lamps ON signal circuit and the Turn Signal Switch headlamps ON signal circuit are grounded. The BCM responds to the inputs by sending a serial data message to the Lighting Control Module, the Lighting Control Module then sends a pulse width modulated voltage signal to the headlamp assembly. The headlamp assembly responds by illuminating the respective LED(s). If serial data communication is lost between the Lighting Control Module and BCM, all Park, Tail, Low Beams and License Plate Lamps will default on with the vehicle in service mode.