System Outline
WARNING: This page is about a different car, the 2008 Lexus LS 600hL. However, it is still accessible from the selected car via links, so may be relevant.
Shift Lock Mechanism
If the brake pedal is depressed and the power switch is changed to the ON (IG) position, the shift lock control ECU is activated, allowing the driver to change the shift lever to a position other than the P position.