Circuit/System Description
WARNING: This page is about a different car, the 2008 Buick LaCrosse and 2008 Buick Allure. However, it is still accessible from the selected car via links, so may be relevant.
When the transmission range selector is placed in the REVERSE position, a serial data message is sent from the powertrain control module (PCM)/engine control module (ECM) to the body control module (BCM). The BCM then applies voltage to the left and right backup lamps through the backup lamp supply voltage circuit.