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:
How to Check Lubricant
2500HD with 6.0 L
All Other Series and Engines
To get an accurate reading, the vehicle should be on a level surface.
• For all 4.3 L, 4.8 L and 5.3 L 1500 Series applications, the proper leve ...
Cleaning the Mirror
Do not spray glass cleaner directly on the mirror. Use a soft towel dampened
with water. ...
What to Use
WARNING
Adding only plain water or some other liquid to the cooling system can be dangerous. Plain water and other liquids, can boil before the proper coolant mixture will.
The coolant warning syste ...