GM Service Manual Online
For 1990-2009 cars only

The ignition lock module controls the shift lock solenoid through a low side drive control circuit. When the ignition is on and the shift lever is in the park position, the ignition lock module will energize the shift lock solenoid by grounding the control circuit. The stop lamp switch signal provides an input to the ignition lock module and when the brake pedal is pressed, the ignition lock module will de-energize the shift lock solenoid.