Parental Control
The RSE system may have a Parental Control feature, depending on the radio. To enable Parental Control, press and hold the radio power button for more than two seconds to stop all system features such as: radio, video screen, RSA, DVD and/or CD.
While Parental Control is on, 
displays.
When the radio is turned back on, Parental Control is unlocked.
See also:
Online Owner Center
Manage your vehicle (U.S.) at gmc.com. Click on “Owners,” then “Manage My GMC/Owners Login.”
Information and services customized for your specific vehicle — all in one convenient place.
...
Engine Identification
The eighth character in the VIN is the engine code. This code identifies the
vehicle's engine, specifications, and replacement parts. See “Engine Specifications”
under Capacities and Speci ...
Playing a DVD
DVD/CD AUX (Auxiliary): Press to cycle through DVD, CD, or Auxiliary when listening to the radio. The DVD/CD text tab and a message showing the track or chapter number will display when a disc is in e ...