Circuit Description
WARNING: This page is about a different car, the 2005 Buick LaCrosse and 2005 Buick Allure. However, it is still accessible from the selected car via links, so may be relevant.
The body control module (BCM) has an internal battery voltage sensor and a reference voltage. The BCM compares these 2 voltages via the 2 battery positive voltage circuits every 300 milliseconds.