The headlights are controlled by the body control module (BCM) via the Headlamp Relay when the headlamp and panel dimmer switch is the AUTO position. When in the AUTO mode, the BCM receives a signal, (voltage) from the ambient light sensor, based on the voltage on the sensor the BCM turns the day time running lamp (DRL) lights OFF and the headlights ON. The headlights can also be turned on by placing the headlamp and panel dimmer switch in the head position.
The relay coil is fed by the headlamp and panel dimmer switch or the BCM and the battery B+ buss bar in the engine wiring harness junction block. The BCM supplies current to the relay based on the input from the ambient light sensor via CKT 352.
The relay output feeds the LT HDLP and RT HDLP fuses to supply current to the low and high beam lamps on CKT 1340 and CKT 1240. The ground for both the low and high beam lamps is supplied via CKT 524 and CKT 525 to the dimmer switch. The dimmer switch uses CKT 1850 for a ground to G203.
Some circuits are monitored by the BCM, and upon failure may set a DTC.
The automatic lamp control (ALC) system and the DRL feature can be temporarily disabled by performing the following procedure:
Note: The ALC and DRL cannot be turned off on the Canadian vehicles and some early production vehicles.
- Turn the ignition to RUN.
- Press the DOME OVERRIDE button four times within six seconds.
A chime will sound informing you that the system is off. The system will remain disabled until the ignition is cycled off and then on or by pressing the DOME OVERRIDE button four more times within six seconds. The chime will sound again signaling that the system has been reactivated.
