Shift Interlock: Description and Operation

The Brake Transmission Shift Interlock (BTSI) is designed to prevent shifting out of "PARK" without pressing on the brake pedal. BTSI Solenoid is energized when the Ignition Switch is in "RUN," "BULB TEST" or "START" and is de-energized when the brake pedal is depressed. The Stoplamp/Torque Converter Clutch Switch receives Ignition voltage from Fuse 39 in "RUN," "BULB TEST" or "START." The Stoplamp Switch is normally closed, providing voltage through CKT 420 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 Stoplamp Switch opens, removing voltage from CKT 420 to the BTSI Solenoid. This de-energizes the BTSI Solenoid, allowing the Shift Lever to be moved out of the "PARK" position. A Park Position Switch is used on column shifted vehicles to interrupt CKT 420 to the BTSI Solenoid once the Transaxle is shifted Out of "PARK." On console shifted vehicles, the BTSI Solenoid is always energized but not mechanically engaged once the Transaxle is shifted from "PARK."