1. Run the engine for one to two minutes and then turn it off. Depress the brake pedal several times with normal braking force. If the first time you press the brake pedal, it is squeezed out to the maximum, and with subsequent presses, its stroke gradually decreases, then the vacuum booster is working normally. If, with successive pressing of the pedal, its stroke remains unchanged, then the vacuum brake booster is faulty.
2. With the engine off, 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 is slightly lowered, then the vacuum booster is working. If, after starting the engine, the pedal remains in place, then the vacuum booster is faulty.
3. With the engine running, depress the brake pedal and then stop the engine. Hold the brake pedal depressed for 30 seconds. If the position of the pedal does not change, then the vacuum brake booster is working. If the brake pedal rises, then the vacuum booster is faulty.
4. If the results of one of the checks carried out were unsatisfactory. then you should look for a malfunction in the hoses or the vacuum brake booster. Make any necessary repairs. If the results of all checks are normal, then the amplifier is working.