Circuit Description
WARNING: This page is about a different car, the 2007 Hummer H2. 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 sends a variable voltage signal to the body control module (BCM) in response to the exterior light level. The BCM energizes the daytime running lamp (DRL) relay by grounding the DRL relay control circuit. The DRL operate when the ambient light sensor indicates daytime, the ignition switch is in the RUN position, and the gear selector is not in the park position.