For 1990-2009 cars

1. Block the wheels.
2. Start the engine.
3. Charge the system air pressure to the governor cut-out point.
4. Have an assistant apply the brakes hard and then release them several times.
5. Check that the brakes apply and release promptly at each wheel.
6. Replace or overhaul the valve (5) if the brakes do not release promptly. Refer to Rear Air Brake Relay Valve Replacement or Air Brake System Description and Operation .
7. Remove the wheel blocks.