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:
Roadside Assistance Program
U.S.: 1-888-881-3302
TTY Users (U.S.): 1-888-889-2438
Canada: 1-800-268-6800
Mexico: 01-800-466-0801
As the owner of a new GMC, you are automatically enrolled in the Roadside Assistance program.
...
Customer Assistance Offices (Mexico)
To contact the Customer Assistance Center (CAC), use the phone numbers listed in this section.
Customer assistance is available Monday through Friday, 08:00 to 20:00 hours, and Saturdays from 08:00 t ...
Playing a DVD
(Tune): Turn to change tracks on a CD or DVD, to manually tune a radio station, or to change clock or date settings, while in the clock or date setting mode. See the information earlier in this secti ...