GMC 2011 Sierra Owner's Manual page 375

This message can display
when the system is not receiving
information it requires from other
vehicle systems.
If any other problem occurs or if a
problem persists, see your dealer.
The rear vision camera is located in
the bezel for the tailgate handle.
The camera uses a special lens.
The distance of the image that
appears on the screen differs from
the actual distance. The area
displayed by the camera is limited.
The camera does not display
objects which are close to either
corner of the bumper or under the
bumper. The area displayed on
the screen can vary according
to vehicle orientation or road
conditions.
The following illustration shows
the field of view that the camera
provides.
A. View displayed by the camera
B. Corner of the rear bumper