Description & Operation: Introduction

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 gearshift lever out of the PARK position. The system consists of the following components:

• The automatic transmission (A/T) shift lock control solenoid.
• The automatic transmission (A/T) shift lock control switch (stoplamp switch).
• The body control module (BCM).
• The powertrain control module (PCM).

With the ignition in the ON position, the PCM sends the transmission gear position to the BCM through a class 2 message. When the BCM receives the message that the transmission is in the PARK position, the BCM energizes the park/neutral position (PNP) switch park signal circuit. Battery voltage is supplied to the stoplamp switch and flows through the normally closed contacts of the switch to the A/T shift lock control solenoid. The A/T shift lock control solenoid is permanently grounded and therefore energizes, locking the gearshift lever in the PARK position. When the driver presses the brake pedal, the contacts in the stoplamp switch open. This causes the A/T shift lock control solenoid to de-energize, allowing the driver to move the gearshift lever out of the PARK position. With the gearshift lever out of the PARK position, the PCM sends a class 2 message to the BCM indicating the transmission is out of the PARK position. The BCM then de-energizes the PNP switch park signal circuit.