Order of execution
1. Start the engine and stop it after 1-2 minutes. Depress the brake pedal 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.
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.
3. Start the engine.
Depress the brake pedal with normal force. Stop the engine. Slowly depress the brake pedal and keep it depressed for 30 seconds. If the pedal height does not change, the brake booster is working properly.
Otherwise, check the one-way vacuum valve or vacuum hose for damage and check that they are secure.