Automatic Transmission Shift Lock Control Description and Operation (With T4Z)

The automatic transmission park lock control system is a safety device that prevents an inadvertent shift out of PARK. Vehicles equipped with the Safety Belt Assurance System (RPO T4Z), the driver must press the brake pedal and have the driver and if present, the front outboard passenger safety belt(s) buckled 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), 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 inflatable restraint sensing and diagnostic 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.
• The inflatable restraint sensing and diagnostic module determines if the occupied driver and front outboard passenger, if present, have their safety belt(s) buckled.

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.

Vehicles with the Safety Belt Assurance System, will display the following message "Shift Locked, Buckle Seatbelt" if the driver and front outboard passenger, if present, do not have safety belt(s) buckled. The vehicle will not shift out of PARK. Buckle the safety belt(s) to unlock the shifter.

This system may not allow the vehicle to shift out of PARK if an object such as a briefcase, handbag, grocery bag, laptop, or other electronic devices is on the front outboard passenger seat. If this happens, remove the object from the seat or buckle the safety belt.

Vehicles with the Safety Belt Assurance System, will display the following message "Shift Unlocked, Brake To Shift" if the system times out and allows the vehicle to be shifted out of PARK after 30 s following brake applied.

The Safety Belt Assurance System can be disabled with a calibration file update in the K36 Inflatable Restraint Sensing and Diagnostic Module using SPS. This procedure should only be done to help resolve a customer dissatisfaction issue.