Brake pedal sound

2001 MAZDA TRIBUTE
217,875 MILES • 3.0L • 6 CYL • 2WD • AUTOMATIC
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ROND225
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I am hearing a hissing sound (like an air leak) under dash by brake pedal. It stops when pressing on the brake pedal. Could it be a faulty brake booster?
May 31, 2022 at 3:27 PM
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STEVE W.
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It could be. To test it the simple way, unplug the vacuum line that goes to the booster and block it off. Then start the engine and see if the hissing goes away. If it has then the booster will need to be replaced. Attached are the instructions.
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May 31, 2022 at 8:57 PM