Diagnostics
OnStar Vehicle Diagnostics will perform a vehicle check every month. It will check the engine, transmission, antilock brakes, and major vehicle systems. It also checks the tire pressures, if the vehicle is equipped with the Tire Pressure Monitoring System. If a diagnostics check is needed between e-mails, push 
, and an Advisor can run a check.
See also:
When to Check and Change Automatic Transmission Fluid
A good time to check the automatic transmission fluid level is when the engine oil is changed.
Change the fluid and filter at the intervals listed in Maintenance Schedule on page 11‑3 and be su ...
Before Driving Off-Road
• Have all necessary maintenance and service work completed.
• Fuel the vehicle, fill fluid levels, and check inflation pressure in all tires, including the spare, if equipped.
• Read all the ...
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 ...