Brake Shift Interlock Operation
WARNING: This page is about a different car, the 2014 Ford Explorer. However, it is still accessible from the selected car via links, so may be relevant.
When the ignition switch is in RUN/START, the solenoid inhibits the selector lever movement (from the PARK position) if the brake pedal is not pressed.
The BSIA inhibits the selector lever movement from the PARK position by mechanically blocking the detent pawl of the selector lever mechanism. When the brake pedal is applied with the ignition key in the RUN/START position and the transmission in PARK, the BSIA is energized by the BCM-B , this allows the selector lever to be moved out of the PARK position.