See also:

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 ...

Warranty
OnStar equipment may be warranted as part of the new-vehicle limited warranty. The manufacturer of the vehicle furnishes detailed warranty information. ...

Adjusting the Speakers (Balance/Fade)
BAL/FADE (Balance/Fade): To adjust the balance or fade: 1. Press until the speaker control tabs display. 2. Continue pressing to highlight the tab, or press the softkey under the tab. 3. To adju ...