Daytime Running Lamp: Description and Operation

DAYTIME RUNNING LAMPS (DRL)

The ambient light sensor is a light-sensitive transistor that varies its voltage signal to the body control module (BCM) in response to changes in the outside (ambient) light level. When the BCM receives this signal the BCM either turns on the just the low beam headlamps for the daytime running lamp (DRL) operation or turns on the low beam headlamps and the exterior lamps for automatic lamp control (ALC). Any function or condition that turns on the headlamps will cancel the DRL operation. Thirty seconds after you start the engine with the headlamp switch in the OFF position, the DRL will perform one of two actions:
- Illuminate the low beam headlamps in daylight conditions.
- Illuminate the low beam headlamps and exterior park lamps for low light conditions.

The DRL/EXT Fuse in the top underhood junction block supplies battery positive voltage at all time to the coil side of DRL relay, left low and high beam headlamps. When the DRL ambient light sensor indicates a daylight condition, the BCM energizes the DRL relay allowing ground from G101 through the switched side of the DRL relay to the left and right low beam headlamps. The DRL operates when the ignition switch is in the RUN position, the parking brake is not set and the transmission is not in the PARK position When these conditions are met and the DRL ambient light sensor indicates daylight conditions the DRL will illuminate.