How to Diagnose Power Brake Booster Problems

Written by cecil fontaine
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How to Diagnose Power Brake Booster Problems
Learn how to troubleshoot power brake boosters. (Car Brake image by Joelyn Pullano from

Since the introduction of disc brakes, the vast majority of modern vehicles operate with power brake boosters. Boosters increase the force applied to your car's brakes by using a vacuum created by the engine. This allows the brake system to multiply the force exerted by the driver on the brake pedal into the force necessary to slow down or completely stop the car. Like any other car component, power brake boosters undergo normal wear and tear, and learning to recognise when they are going bad is vital to safe driving.

Skill level:


  1. 1

    Turn off your car and pump your brake pedal five times. Push the brake pedal all the way down and turn the car on, keeping the pedal pushed down while starting the car. If your brake booster is functioning normally, you should notice that the pedal goes further down and the resistance will immediately decrease. If the pedal's position does not change and the resistance does not change, this indicates a faulty power brake booster.

  2. 2

    Leave your car running for five minutes. Turn it off and immediately push the brake pedal five times. If the brake booster is functioning normally, you should notice that the resistance increases each time you push the brake down. In addition, the pedal should come to a rest at a higher level after each push of the brake pedal. If you do not observe this happening, the power brake booster is malfunctioning.

  3. 3

    Listen for any whining noises that occur when you apply the brakes while driving your car. If you notice this, the vacuum line that connects to the power brake booster is punctured and is letting air out, resulting in whining when the brake is applied. In this case, the vacuum line must be replaced to prevent the brake booster from failing.

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