Function Test

1.Make sure the engine is stopped/off, pump the brake pedal 4-6 times, than pump the pedal hard and hold the pressure for 15 seconds. If the pedal sinks, your master cylinder, brake line or brake calliper is faulty.
2.Get the engine running, if the pedal drops slightly, the booster us working. If the pedal does not drop the booster or check value is faulty.

Leak Test

1.While the engine is running pump the pedal and than turn the engine off. If the pedal does not drop after holding the pedal down for 30 seconds the booster is fine. If the pedal rises, the booster is faulty.

2.With the engine off, pump the pedal 4 to 6 times with little amount of pressure, it should be low. Pedal should increase. If not check the booster check value.