GM Service Manual Online
For 1990-2009 cars only

The vehicle is programmed so that when the shift lever is moved into (P) Park for automatic transmission vehicles or when the ignition is turned off or is in Retained Accessory Power (RAP) for manual transmission vehicles, both doors will unlock.

With the vehicle stopped and the engine running, door unlocking can be programmed through the Driver Information Center (DIC). This allows the driver to choose various unlock settings. For programming information, see DIC Vehicle Personalization.