GM Service Manual Online
For 1990-2009 cars only

The vehicle's doors are programmed from the factory to lock when the shift lever is moved into a forward gear, and to unlock when the shift lever is moved into PARK (P).

If someone needs to get in or out of the vehicle after the doors have been locked, place the shift lever into PARK (P). You may also unlock all doors using the power door lock switch or unlock one door using the inside manual door lock.

To program the door unlocking feature, see "Personal Programming Mode Screens" under DIC Vehicle Customization . The locking feature cannot be disabled or programmed.