Shift Interlock: Description and Operation

Automatic Transmission Shift Lock Control Description and Operation Description
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 switch
- The automatic transmission shift lock control solenoid
- The body control module (PZM)
- The PARK relay
- The powertrain control module (PCM)
With the ignition in the ON position, the PCM sends a class 2 serial data message to the PZM indicating the transmission gear position. With the transmission in the PARK position the PZM supplies a ground to the PARK relay control circuit. This energizes the PARK relay coil and closes the switch contacts. With the contacts closed, voltage is supplied from the PARK relay battery voltage circuit through the normally closed contacts of the automatic transmission shift lock control switch, to the automatic transmission shift lock control solenoid. The permanently grounded automatic transmission shift lock control solenoid energizes, mechanically locking the transmission shift lever in the park position. When the driver presses the brake pedal 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 moved out of the PARK position.