GM Service Manual Online
For 1990-2009 cars only

If your vehicle has an automatic transmission, it is programmed from the factory to lock the doors automatically when the shift lever is moved out of PARK (P). All the doors will unlock when the shift lever is moved back into PARK (P).

If your vehicle has a manual transmission, it is programmed from the factory to lock the doors automatically when the vehicle speed is greater than 15 mph (24 km/h). The doors will unlock when the key is removed from the ignition.

To personalize the automatic door locks, see "Automatic Door Locks" under DIC Operation and Displays .