Automatic Transmission Shift Lock Control Description and Operation

The automatic transmission park lock control system is a safety system that prevents accidental shifting from the PARK position. The driver must depress the brake pedal before the park lever can be moved from the PARK position. The system consists of the following components:

• The automatic transmission park lock solenoid (serviced as the automatic transmission shift lock actuator), is located within the floor shift control assembly.
• 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 energizes. When the brake pedal is not applied, the body control module turns the control voltage output of the park lock control solenoid OFF, de-energizing the park lock control solenoid. The de-energized solenoid mechanically locks the park lever in the PARK position.