Circuit/System Description
WARNING: This page is about a different car, the 2015 Cadillac SRX. However, it is still accessible from the selected car via links, so may be relevant.
When the vehicle is placed in reverse with the engine running, a voltage signal is sent to the rearview camera to turn on and send a video signal to the Human Machine Interface Control Module. If the Human Machine Interface Control Module does not see a signal from the camera it will set B127B 2B and display "Service Rear Vision System".