2010 GMC Sierra 1500 Crew Cab Owner's Manual - Page 151

Lockout Protection This feature protects you from locking the key in the vehicle when the key is in the ignition and a front door is open. If the driver's side power door lock switch is pressed when the driver's door is open and the key is in the ignition, all of the doors will lock and then the driver's door will unlock. If the passenger's side power door lock switch is pressed when the front passenger's door is open and the key is in the ignition, all of the doors will lock and then the front passenger's door will unlock. Rear Doors Extended Cab Your vehicle may have a rear access door(s) that allows easier access to the rear area of the extended cab. 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. You must fully close a rear access door before you can close the front door. 3-13