GM Service Manual Online
For 1990-2009 cars only
Park Brake Solenoid A Command: The scan tool displays Off or On. The state that the BCM is commanding the park brake relay A.

Park Brake Solenoid B Command: The scan tool displays Off or On. The state that the BCM is commanding the park brake relay B.

Park Brake Switch: The scan tool displays Off or On. The status of the park brake switch signal.