Circuit Description
WARNING: This page is about a different car, the 2006 Pontiac Montana SV6, 2006 Chevrolet Uplander, and 2006 Buick Terraza. However, it is still accessible from the selected car via links, so may be relevant.
The body control module (BCM) has an internal voltage sensor with a dedicated circuit that checks the battery positive voltage and battery negative circuit voltage to determine if it is below 15.5 volts.