Circuit/System Description
WARNING: This page is about a different car, the 2016 GMC Acadia, 2016 Chevrolet Traverse, and 2016 Buick Enclave. However, it is still accessible from the selected car via links, so may be relevant.
When the PRNDL is placed in the REVERSE position, a serial data signal is sent from the transmission control module (TCM) to the body control module (BCM). The BCM then applies voltage through the backup lamps control circuit to the tail lamp assemblies illuminating the backup lamps. The engine may need to be running for the backup lamps to function.