Speed-sensitive Automatic Door Lock Function by Vehicle Speed does not Work: Description
WARNING: This page is about a different car, the 2007 Lexus SC 430. However, it is still accessible from the selected car via links, so may be relevant.
The theft warning ECU monitors vehicle speed signals transmitted from the meter ECU, and it will drive each door lock motor when any of the doors is in the unlocked state with the vehicle speed at approximately 20 km/h (13 mph).