Doors automatically lock with the keys in the ignition and running locking in anyone who is still in vehicle who cannot open to door physically. It will also prevent you from entering the vehicle without a second set of keys or other methods of unlocking the door (onstar, locksmith). This could put occupants in danger and exposed to the elements unexpectedly and also place inside children in danger. Diagnosis — Keyfob — If battery in keyfob is low, the programming of the vehicle is set to automatically lock even if vehicle is in the ignition and running. when unlocking vehicle with the defective fob, vehicle will unlock, then immediately lock preventing entry. Remedy — Replace battery in key fob and truck works as normal.