Key Cylinder Unlock
WARNING: This page is about a different car, the 2004 Pontiac Aztek and 2004 Buick Rendezvous. However, it is still accessible from the selected car via links, so may be relevant.
This feature will unlock all of the doors when the BCM receives a KEYUNLK input signal for greater than 1 second. This feature is disabled from the factory and can be enabled using a scan tool.