GM Service Manual Online
For 1990-2009 cars only

Lockout protection is intended to provide additional security and convenience. While any door is open and the key is in the ignition, the doors cannot be locked by using the power door locks.

To override this feature, while 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 the key is not 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.