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 engine control module (ECM)
• The transmission control module (TCM)

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 ECM sends a serial data message to the BCM indicating the transmission is in the PARK position.
• The ECM receives a brake applied input from the brake light switch and sends a serial data message to the BCM indicating the brakes are not applied.

With the above conditions met, the BCM supplies battery voltage to the shift lock control solenoid. The solenoid is permanently grounded and therefore energizes, locking the shift lever in the PARK position. When the brake pedal is depressed the ECM send a serial data message to the BCM indicating the brakes are applied. The BCM turns off the battery voltage supply to the shift lock control solenoid. This de-energizes the shift lock control solenoid releasing the mechanical lock, allowing the driver to move the shift lever out of the PARK position. With the shift lever out of the PARK position the ECM sends a serial data message to the BCM and no voltage is applied to the shift lock control solenoid.