Shift Interlock: Description and Operation

The brake transmission shift interlock (BTSI) is designed to prevent shifting out of PARK without depressing the brake pedal. The BTSI actuator is energized when the ignition switch is in RUN, BULB TEST, or START and is de-energized when the brake pedal is depressed. The stop lamp switch receives ignition voltage in RUN, BULB TEST, or START from the IGN 1 Fuse. The stop lamp switch is normally closed, providing voltage through circuit 1135 to the BTSI actuator, 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 actuator. This de-energizes the BTSI actuator, allowing the shift lever to be moved out of the PARK position.