Circuit Description

WARNING: This page is about a different car, the 2003 GMC Sierra, 2003 GMC Cab & Chassis Sierra, 2003 Chevrolet Silverado, and 2003 Chevrolet Cab & Chassis Silverado. 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 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, the gear selector is not in the park position, and the parking brake is in released. The DRL can be manually turned OFF by depressing the AHL/DRL DEFEAT switch in the headlamp switch. The AHL/DRL defeat switch sends a ground signal through the DRL switch signal circuit to the BCM. The BCM then turns OFF the DRL and turns ON the DRL OFF lamp in the headlamp switch by grounding the DRL OFF indicator control circuit.