Automatic Transmission Shift Lock Control Description and Operation

The automatic transmission park 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 park lever out of the PARK position. The system consists of the following components:

• The automatic transmission park lock solenoid (serviced as the automatic transmission shift lock actuator), located within the floor shift control assembly with vehicles equipped with floor shift.
• The body control module, which controls the voltage supply circuit of the park lock control solenoid.
• The engine control module.

The body control module controls the voltage to the park lock control solenoid through the park lock control solenoid controlled voltage circuit. The following conditions must be met before the body control module will supply voltage to the park lock solenoid:

• The ignition is in the ON position.
• The engine control module sends an input via GMLAN serial data to the body control module indicating the transmission is in the PARK position.
• The body control module determines the brake pedal is applied according the brake pedal position.

Since the park lock control solenoid is permanently grounded, the body control module supplies voltage to the automatic transmission park lock control solenoid, unlocking the park lever allowing the driver to move the park lever out of the PARK position as the solenoid de-energizes. When the brake pedal is not applied, the body control module turns the control voltage output of the park lock control solenoid OFF, energizing the park lock control solenoid. The energized solenoid mechanically locks the park lever in the PARK position.

During remote start operation, the body control module will energize the park lock control circuit, locking the park lever in the PARK position.