Unable to Connect to OnStar Message
If there is limited cellular coverage or the cellular network has reached maximum capacity, this message may come on. Push 
to try the call again or try again after driving a few miles into another cellular area.
See also:
Rear Vision Camera (RVC)
The vehicle may have a rear vision camera system. Read this entire section before using it.
WARNING
The RVC system does not display pedestrians, bicyclists, animals, or any other object located outs ...
Customer Assistance Offices (U.S. and Canada)
GMC encourages customers to call the toll-free number for assistance.
However, if a customer wishes to write or e-mail GMC, the letter should be addressed to:
United States
GMC Customer Assistance ...
Rear Vision Camera Error Messages
SERVICE REAR VISION CAMERA SYSTEM: This message can display on the radio screen
when the system is not receiving information it requires from other vehicle systems.
If any other problem occurs or i ...