2. Apply the parking brake.
3. Release the air from the air system by opening the drain cock on the air tank.
4. Wait 5 minutes.
5. If the spring brakes have come on, the wheels will be locked and the vehicle will be unable to move.
Note: Be sure to park the vehicle on a level surface so that the spring brakes can engage fully. If the vehicle is parked on a hill, the spring brakes may not come on properly and the vehicle could roll away.