Shift Interlock: Description and Operation

Automatic Transmission Shift Lock Control Description and Operation

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 thew following components:

* The automatic transmission shift lock control solenoid
* The body control module (BCM)
* The engine control module (ECM)

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

* The ignition is in the ON position
* The ECM sends an input via GMLAN serial data to the BCM when the transmission control module (TCM) indicates the transmission is in the PARK position
* The BCM receives a brake applied input from the brake light switch

Since the shift lock control solenoid is permanently grounded, the BCM supplies voltage to the automatic transmission shift lock control solenoid, releasing the mechanical lock on the shift lever as the solenoid energizes. The energized solenoid allows the driver to move the shift lever out of the PARK position. When the brake pedal is not applied, the BCM turns the control voltage output of the shift lock control solenoid OFF, de-energizing the shift lock control solenoid. When the transmission is in the PARK position, the de-energized shift lock control solenoid will prevent shifting as the lever is mechanically locked in the PARK position. During remote start operation the BCM will de-energize the automatic transmission shift lock control circuit, locking the shift lever in the PARK position.