Checking the operation of the brake booster (Hyundai Sonata EF)

1. Run the engine for one or two minutes and then turn it off. Press the brake pedal several times with the usual force when braking. If the first time you press the brake pedal, it is pressed to the maximum, and with subsequent presses, its travel gradually decreases, then the vacuum brake booster is working normally. If its travel remains unchanged with successive presses of the pedal, then the vacuum brake booster is faulty.



2. With the engine not running, press the brake pedal several times and make sure that the brake pedal travel changes. Then, without releasing the brake pedal, start the engine. If the brake pedal drops slightly, the vacuum booster is working properly. If the pedal remains in place after starting the engine, the vacuum booster is faulty.

3. With the engine running, press the brake pedal and then turn off the engine. Keep the brake pedal pressed for 30 seconds. If the pedal position does not change, the brake booster is OK. If the brake pedal rises, the brake booster is faulty.



4. If the results of one of the tests are unsatisfactory, then you should look for a fault in the hoses or the brake booster. Perform the necessary repairs. If the results of all tests are normal, then the booster is in good working order.

[The text is taken from an online source HyundaiBook.ru]