GM Service Manual Online
For 1990-2009 cars only

If the vehicle has power door locks and the remote keyless entry system, it has an automatic lock/unlock feature.

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

If the vehicle has a manual transmission, it is programmed from the factory to lock all the doors 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 change the automatic door lock and unlock settings, see "Automatic Door Locks" under DIC Operation and Displays .