How to Diagnose a Bad Brake Booster

Written by cheryl macman
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How to Diagnose a Bad Brake Booster
(Hemera Technologies/ Images)

A brake booster is a cylinder set-up that can be installed to reduce the required amount of force upon the brake pedal to initiate the braking function. If you are having any trouble with your brake performance, a bad brake booster may be the cause of it. There is a simple way to diagnose whether your brake booster is to blame or if it is still functioning properly, while a different part of the brakes is causing problems.

Skill level:


  1. 1

    Turn off the engine in the car and let the engine cool down completely. Sit in the car so you can easily reach the pedals.

  2. 2

    Put your foot on the brake pedal and push the pedal down all the way. This will work out some of the remaining air vacuum in the brake booster.

  3. 3

    Release and press down the pedal again three more times to rid the entire vacuum. Hold the pedal down when you finish pumping the brake.

  4. 4

    Turn the engine on while holding down the pedal and monitor the movement of the pedal. If you feel the pedal move in upon starting, the booster is fine. If there is no movement in the pedal, the booster is bad.

Tips and warnings

  • Have all of your systems in the car checked often by a qualified mechanic to diagnose failure before it affects your safety.
  • Do not drive a car if you are unsure of the integrity of the brake system and its components.

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