The valve has a yellow diamond-shaped control knob. The vehicle park brake is applied when the knob is pulled out. Pushing the knob in releases the park brake actuator.

The knob will stay pushed in as long as the supply pressure is 414 kPa (60 psi) or more. When the air pressure drops below 414 kPa (60 psi), the valve spring causes the knob to pop out.

The park brake valve has a supply port, a delivery port, an exhaust port, and a control knob with a pop-out spring. When the knob is pulled out, the supply port is blocked and the delivery ports vent to the exhaust port. When the knob is pushed in, the exhaust port is blocked and the supply air flows out of the delivery port.

The park brake lamp on the instrument cluster turns on when the parking brake is applied.

The pressure sensor is located at the park brake valve assembly. The sensor serves as the device to turn on the park brake lamp when the parking brake is applied and turn it off when the parking brake is released. The sensor is normally closed and opens when air pressure is present in the line.

The park brake actuator has a long mechanical spring that forces the pushrod outward when the air pressure is exhausted. Releasing the parking brake involves sending air pressure to the park brake actuator. The air pressure compresses the spring in the park brake actuator in order to release the parking brake.