Circuit Description
WARNING: This page is about a different car, the 2002 GMC Safari and 2002 Chevrolet Astro. However, it is still accessible from the selected car via links, so may be relevant.
The body control module (BCM) monitors the ambient light sensor signal circuit in order to determine if the daytime running lights (DRL) or the auto headlights (ALC) should be turned ON in the AUTO mode. When the BCM senses the ambient light sensor voltage is between 1.7 volts and 4.7 volts, the DRL will be commanded ON. When the BCM senses the ambient light sensor voltage between 0.2 volts and 1.0 volts, the ALC will be commanded ON.