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

Park Brake Relay - B: The scan tool displays Off or On. The state that the RIM 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.