Circuit/System Verification
WARNING: This page is about a different car, the 2011 GMC Acadia, 2011 Chevrolet Traverse, and 2011 Buick Enclave. However, it is still accessible from the selected car via links, so may be relevant.
Ignition ON, command the backup lamps ON and OFF with a scan tool. The backup lamps should turn ON and OFF when changing between the commanded states.