Description & Operation: Introduction

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

• Shift lock solenoid (also known as "BTSI solenoid" or "actuator").
• Shift lock control switch (stoplamp switch).
• Park/Neutral Position (PNP) switch.

With the ignition switch in the ON position, battery positive voltage is supplied to the PNP switch. When the transmission is in Park, the contacts in the PNP switch are closed. This allows current to flow through the switch to the stoplamp switch. The circuit continues through the normally closed switch to the shift lock solenoid. The shift lock solenoid is permanently grounded. This energizes the shift lock solenoid, mechanically locking the shift linkage in the Park position. When the driver presses the brake pedal, the contacts in the stoplamp switch open causing the shift lock solenoid to de-energize. This allows the gearshift lever to move from the Park position.