Brake Shift Interlock System
WARNING: This page is about a different car, the 2016 Ford Transit Connect. However, it is still accessible from the selected car via links, so may be relevant.
The brake shift interlock actuator (BSIA) inhibits the selector lever movement from the P position by mechanically blocking the detent pawl of the selector lever mechanism. When the brake pedal is pressed (BPP switch closed) with the ignition key in the RUN/START position and the transmission in P, the BSIA is energized by the BCM, this allows the selector lever to be moved out of the P position.