1. Let the engine run for 1 or 2 minutes and then turn it off. Press the brake pedal several times with normal force. If the pedal goes far down when first pressed, but gradually rises after the second or third press, this means the brake booster is working normally.
2. With the engine off, press the brake pedal several times. With the pedal depressed, start the engine. If the pedal drops without effort, the booster is working properly.
3. With the engine running, press the brake pedal and then turn off the engine. Keep the pedal pressed for 30 seconds.
If the pedal height does not change, the brake booster is working properly. If any of the above three operations fails, check the vacuum hoses and brake booster, and then perform the necessary operations.