1. Start the engine and stop it after 1-2 minutes. Depress the brake pedal several times with normal force. If the first stroke of the pedal is long and the second stroke is shorter than the first stroke, this indicates the normal operation of the brake booster (pic. 15.9). If the pedal height does not change, then the vacuum booster is damaged.
Pic. 15.9. Checking the vacuum brake booster after starting and stopping the engine
Pic. 15.10. Checking the vacuum brake booster after starting the engine
2. With the engine off, press the brake pedal several times. Start the engine. If the brake pedal moves down Immediately after starting the engine, this indicates normal operation of the brake booster. If the pedal height does not change, then the vacuum booster is damaged.
3. Start the engine. Depress the brake pedal with normal force. Stop the engine. Slowly depress the brake pedal and hold it down for 30 seconds. If the pedal height does not change, the vacuum brake booster is working properly (pic. 15.11).
Pic. 15.11. Checking the vacuum brake booster after turning off the engine
Otherwise, check the one-way vacuum valve or vacuum hose for damage and check that they are secure.