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. The 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 Brake Switch Assembly receives Ignition Voltage from the Turn B/U Fuse in "RUN," "BULB TEST" or "START." The BTSI Switch is part of the Brake Switch Assembly and is normally closed, providing voltage through CKT 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 BTSI Switch opens, removing voltage from CKT 1135 to the BTSI Solenoid. This de-energizes the BTSI Solenoid, allowing the Shift Lever to be moved out of the "PARK" position.