Shift Lock Control System

The automatic transmission shift lock control system is a safety device that prevents an inadvertent shift out of Park when the engine is running. The driver must press the brake pedal before moving the shift lever out of Park position. The system consists of the following components:

• Shift lock solenoid. Also referred to as Brake Transmission Shift Interlock (BTSI) solenoid.
• Park lock solenoid.
• Shift lock control switch (part of stoplamp switch).
• Transmission Range (TR) switch (PNP switch).

With the ignition switch in the ON position, battery voltage is supplied to the stoplamp switch. The circuit continues through the normally closed switch to the shift lock solenoid. The transmission range switch provides a path to ground for the shift lock solenoid in the Park position. With the shift lock solenoid energized, the shift lever is mechanically locked in the Park position. When the driver presses the brake pedal, the contacts in the stoplamp switch open, de-energizing the shift lock solenoid. This allows the shift lever to move from the Park position. When the shift lever is out of the Park position, the controlled ground contacts in the transmission range switch open. This prevents the shift lock solenoid from energizing when the vehicle is out of the Park position.