Recommended Fuel
Use regular unleaded gasoline with a posted octane rating of 87 or higher. If the octane rating is less than 87, an audible knocking noise, commonly referred to as spark knock, might be heard when driving. If this occurs, use a gasoline rated at 87 octane or higher as soon as possible. If heavy knocking is heard when using gasoline rated at 87 octane or higher, the engine needs service.
See also:
Warranty
OnStar equipment may be warranted as part of the new-vehicle limited warranty. The manufacturer of the vehicle furnishes detailed warranty information. ...
Roadside Assistance Program (U.S. and Canada)
For U.S.-purchased vehicles, call 1-888-881-3302; (Text Telephone (TTY): 1-888-889-2438).
For Canadian-purchased vehicles, call 1-800-268-6800.
Service is available 24 hours a day, 365 days a year.
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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 ...