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, observe the BPP Signal parameter in the ECM while applying and releasing the brake pedal. The parameter should change between Applied and Released when changing between the selected states. All brake lights should turn ON and OFF accordingly.