2. With the engine off, press the brake pedal several times until the hissing in the brake booster stops.
3. Press the brake pedal and hold it down.
4. Without releasing the brake pedal, we start the engine on the car.
5. If, immediately after starting the engine, the brake pedal goes down a little, then the vacuum brake booster is working.
6. Otherwise, check the integrity of the vacuum supply hose to the vacuum booster, the tightness of its connection to the intake module and the branch pipe of the vacuum booster check valve. If the hose is serviceable and connected hermetically, the vacuum booster is faulty.
Scheme of the brake system: 1 - brake mechanism of the front left wheel; 2, 6, 12, 17 - brake hoses; 3, 7, 11, 18 - brake pipes; 4 - main brake cylinder; 5 - brake mechanism of the front right wheel; 8 - reservoir of the main brake cylinder; 9 - vacuum brake booster; 10 - brake pedal; 13 - brake mechanism of the rear right wheel; 14 - brake fluid pressure regulator in the brake mechanisms of the rear wheels; 15 - brake fluid pressure regulator lever in the rear wheel brakes; 16 - rear left wheel brake