Circuit/System Verification
WARNING: This page is about a different car, the 2010 Cadillac SRX. However, it is still accessible from the selected car via links, so may be relevant.
Ignition ON, command the E6 center high mounted stop lamp ON and OFF by applying and releasing the brake pedal. The E6 center high mounted stop lamp should turn ON and OFF each time the brake pedal is applied and released.