2012 GMC Sierra Owner's Manual - Page 53

Keys, Doors, and Windows 2-9 Lockout Protection If the driver side power door lock switch is pressed when the driver door is open and the key is in the ignition, all of the doors will lock and then the driver door will unlock. If the passenger side power door lock switch is pressed when the front passenger door is open and the key is in the ignition, all of the doors will lock and then the front passenger door will unlock. Doors Rear Doors (Extended Cab) Safety Locks The vehicle has rear door security locks to prevent passengers from opening the rear doors from the inside. Open the rear doors to access the security locks on the inside edge of each door. To set the locks, insert a key into the slot and turn it to the horizontal position. The door can only be opened from the outside with the door unlocked. To return the door to normal operation, turn the slot to the vertical position. To open a rear access door from the outside, first open the front door. Then, use the handle located on the front edge of the rear access door to open it.