For 1990-2009 cars

1. Apply the parking brake.
2. Start the engine.
3. Charge the system air pressure to the governor cut-out point.
4. Pull out the exposed end of the valve stem.
5. Air should be expelled from the vent.
6. Replace the safety valve (1) if the air is not expelled.
7. Release the valve stem.
8. Check that the air exhaust stops.
9. Replace or overhaul the safety valve (1) if the air does not stop. Refer to Primary Air Brake Supply Reservoir Safety Valve Replacement or Air Brake System Description and Operation .