Automatic Transmission Shift Lock Control System

WARNING: This page is about a different car, the 2007 Saturn Ion 3 and 2007 Saturn Ion 2. However, it is still accessible from the selected car via links, so may be relevant.

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 body control module (BCM)
The transmission control module (TCM)

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 TCM sends a class 2 message to the BCM indicating the transmission is in the PARK position.
The BCM receives a brake applied input from the stop lamp 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. This allows the driver to move the shift lever out of the PARK position. When the brake pedal is not applied, the BCM switches the ground of the shift lock control solenoid OFF, de-energizing the shift lock control solenoid. The de-energized solenoid mechanically locks the shift lever in the PARK position.