2. With the engine off, press the brake pedal several times. 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 brake pedal does not change, then the vacuum brake booster is working. If the brake pedal rises, then the vacuum booster is defective.
4. Analysis of the results of inspections.
A) If the results of all three checks are positive, then the operation of the vacuum brake booster is normal.
b) If the results of one of the tests carried out were unsatisfactory, then you should look for a malfunction in the vacuum hose, non-return valve or vacuum brake booster.