Circuit/System Description
WARNING: This page is about a different car, the 2012 Chevrolet Malibu. 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 the voltage signal to the body control module (BCM) based on outside lighting conditions. When the ambient light sensor indicates daytime conditions, the body control module (BCM) grounds the DRL relay control circuit causing voltage to flow from the DRL fuse which energizes the DRL relay. With the DRL relay energized, the switch contacts close and voltage is applied to the left and right low beam headlamps. Any function or condition that turns on the headlamps will cancel DRL operation.