GM Service Manual Online
For 1990-2009 cars only

If you press the power door lock switch when the key is in the ignition and any door is open, all the doors will lock and then the driver's door will unlock. Be sure to remove the key from the ignition when locking your vehicle.

If the remote keyless entry transmitter is used to lock the doors while the key is in the ignition, a chime will sound three times. All doors will then lock.