Daytime Running Lamps (DRL)

WARNING: This page is about a different car, the 2009 Saturn Vue. However, it is still accessible from the selected car via links, so may be relevant.

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 turns ON just the low beam headlamps at reduced intensity for the daytime running lamp (DRL) operation. A resistor wire is used (CKT312) to reduced the voltage which reduces the light intensity for the DRL's function. The ambient light sensor can also turn 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 (this means no reduced voltage to the low beam lights). 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 at reduced intensity in daylight conditions
Illuminate the low beam headlamps and exterior park lamps for low light conditions

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