GM Service Manual Online
For 1990-2009 cars only

Lockout protection is intended to provide enhanced security and convenience. This feature prevents a driver who has left the key in the ignition from locking the doors, using the power door locks while any door is open.

To override this feature, when the key is in the ignition and any door is open, press and hold down the power door lock switch for three seconds.

This feature cannot guarantee that you will never be locked out of your vehicle. If you don't leave the key in the ignition, or if you use the manual door lock or the remote keyless entry transmitter, you could still lock your key inside your vehicle. Always remember to take your key with you.