Automatic Transmission 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 the PARK position. The system consists of the following components:

• The automatic transmission shift lock control solenoid
• The body control module (BCM)
• The powertrain control module (PCM)

The body control module (BCM) controls the voltage supply circuit of the shift lock control solenoid. The following conditions must be met before the BCM will supply battery voltage to the shift lock control solenoid:

• The ignition is in the ON position.
• The PCM sends a class 2 message to the BCM indicating the transmission is in the PARK position.
• The PCM receives a brake applied input from the stop lamp switch and sends a class 2 message to the BCM indicating the brakes are applied.

With the above conditions met, the BCM supplies battery voltage to the shift lock control solenoid. Since the solenoid is permanently grounded, the solenoid energizes allowing the driver to move the shift lever out of the PARK position. When the brake pedal is not applied, the BCM turns OFF the controlled voltage output to the shift lock control solenoid, de-energizing the shift lock control solenoid. The de-energized solenoid mechanically locks the shift lever in the PARK position.