Shift Interlock: Description and Operation

Automatic Transmission Shift Lock Control Description and Operation
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 automatic transmission shift lock control switch
^ The brake to shift relay
^ The Body Control Module (BCM)
^ The Powertrain Control Module (PCM)

With the ignition in the ON position, voltage is supplied to automatic transmission shift lock control switch and the brake to shift relay coil through the shift lock control voltage supply circuit. The Body Control Module (BCM) supplies a ground for the brake to shift relay when the Body Control Module (BCM) receives a class 2 message from the Powertrain Control Module (PCM) indicating the transmission is in the PARK position. This closes the normally open contacts of the brake to shift relay and grounds the automatic transmission shift lock control solenoid. The normal close contact of the automatic transmission shift lock control switch allows voltage to the automatic transmission shift lock control solenoid. With the brake to shift relay closed the automatic transmission shift lock control solenoid energizes physically locking the shift lever in the PARK position. When the brake pedal is pressed the contacts in the automatic transmission shift lock control switch open, de-energizing the automatic transmission shift lock control solenoid. This allows the shift lever to be move out of the PARK position.

Park Lock Control System (Regal)
The park lock control system is a safety device that prevents an inadvertent shift out of PARK when the ignition is OFF. The system consists of the following components:
^ The automatic transmission park lock solenoid
^ The brake to shift relay
^ The Body Control Module (BCM)
^ The Powertrain Control Module (PCM)

With the ignition in the OFF position the park lock control solenoid is de-energized. This mechanically locks the shift lever in the PARK position. With the ignition in the ON position, battery voltage is supply to the park lock control solenoid. The control circuit of the park lock solenoid is provided a ground through the brake to shift relay when energized. The Body Control Module (BCM) supplies a ground for the brake to shift relay when the Body Control Module (BCM) receives a class 2 message from the Powertrain Control Module (PCM) indicating the transmission is in the PARK position. This closes the normally open contacts of the brake to shift relay and grounds the park lock control solenoid. This energizes the park lock control solenoid releasing the mechanical park lock.