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:
Hill Start Assist (HSA)
This vehicle has a Hill Start Assist (HSA) feature, which may be useful when
the vehicle is stopped on a grade. This feature is designed to prevent the vehicle
from rolling, either forward or rear ...
Storing Radio Stations
Drivers are encouraged to store the radio station while the vehicle is parked; see Defensive Driving on page 9‑3. Tune to stored radio stations using the presets, favorites button, and steering ...
Under the Hood
The Yukon is available with either rear- or four-wheel drive. The Yukon
Denali can have an all-wheel-drive system that's distinct from the available
part-time four-wheel drive on the regular Yukon ...