GM Service Manual Online
For 1990-2009 cars only

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 consist of the following components:

    • The automatic transmission shift lock control solenoid.
    • The automatic transmission shift lock control switch.
    • The transmission range switch.

With the ignition in the ON position, battery positive voltage is supplied to the automatic transmission shift lock control switch. The circuit continues through the normally-closed switch to the automatic transmission shift lock control solenoid. The transmission range switch provides a path to ground in the PARK position. With the automatic transmission shift lock control solenoid energized the shift lever is locked in the PARK position. When the driver presses the brake pedal, the contacts in the automatic transmission shift lock control switch open. This causes the automatic transmission shift lock control solenoid to release. This allows the shift lever to move from the PARK position.