Circuit/System Description
WARNING: This page is about a different car, the 2017 GMC Acadia. However, it is still accessible from the selected car via links, so may be relevant.
Ignition voltage is applied to the rearview camera and send the camera sends a video signal to the Radio or Human Machine Interface Control Module. If the Radio Human Machine Interface Control Module does not see a signal from the camera it will set B127B and display "Service Rear Vision System".