Brake Transmission Shift Interlock (BTSI)

BRAKE TRANSMISSION SHIFT INTERLOCK
The park lock solenoid prevents shifting out of the PARK position when the ignition switch is in LOCK. ACC or OFF. The Brake Transmission Shift Interlock (BTSI) is designed to prevent shifting out of PARK when the ignition switch is in the RUN, BULB TEST, or START position, without pressing the brake pedal. The BTSI solenoid and the park lock solenoid are energized when the ignition switch is in the RUN, BULB TEST, or START position. When the park lock solenoid and the BTSI are energized, the mechanical lock connected to this park lock solenoid is pulled away from the shifter. The stop lamp switch receives ignition voltage in the RUN, BULB TEST, or START position from the BTSI Fuse and is normally closed, providing voltage through circuit 1135 to the BTSI solenoid, energizing the solenoid and mechanically locking the transmission shift lever whenever it is in PARK. When the brake pedal is depressed, the stop lamp switch opens, removing voltage from circuit 1135 to the BTSI solenoid. The BTSI solenoid is de-energized and the mechanical lock connected to the BTSI solenoid pulls back from the shifter allowing shifting.

STEERING COLUMN PARK LOCK
On the Regal with the console shift, there is a lock on the ignition key cylinder, preventing the user from removing the key while in a non-PARK position until the vehicle has returned to the PARK position.