GMC 2011 Sierra Owner's Manual page 377

The RVC system might not work
properly or display a clear image if:
The RVC is turned off.
See Turning the Rear Camera
System On or Off earlier in this
section.
It is dark.
The sun or the beam of
headlights is shining directly
into the camera lens.
Ice, snow, mud, or anything else
builds up on the camera lens.
Clean the lens, rinse it with
water, and wipe it with a soft
cloth.
The back of the vehicle is in an
accident. If this happens, the
position and mounting angle
of the camera can change or
the camera can be affected.
Be sure to have the camera
and its position and mounting
angle checked at your dealer.
The RVC system display in the
rearview mirror may turn off or not
appear as expected due to one
of the following conditions. If this
occurs the left indicator light on
the mirror will flash.
A slow flash may indicate a
loss of video signal, or no video
signal present during the reverse
cycle.
A fast flash may indicate that
the display has been on for the
maximum allowable time during
a reverse cycle, or the display
has reached an Over
Temperature limit.
The fast flash conditions are
used to protect the video
device from high temperature
conditions. Once conditions
return to normal the device will
reset and the green indicator
will stop flashing.
During any of these fault conditions,
the display will be blank and the
indicator will continue to flash as
long as the vehicle is in R (Reverse)
or until the conditions return to
normal.
Pressing and holding
left indicator light is flashing will turn
off the video display along with the
left indicator light.
when the