HISSING NOISE IN BRAKE PEDALS

[StibbyWonder]

Hi everyone.

I would like to ask, where should I start checking this hissing noise near the brake pedals of my Ford Expedition 2003 model XLT. When I drove it or I am just idling for a few minutes my engine check light went on, also the hissing noise will stop if I stepped on the brake pedals. I’ll post the photo of the code P171 & P174 and what was in it.

See photos below for reference:


Based from the above photo it states that System too lean in B1 & B2.







On the photos above are the contents under the P171 code based from the first photo there is a “freeze frame” and here are the datas informing the P171.

I done my research that some guys explaining the hissing noise is coming from the brake booster in the engine bay, they saying I need to replace it. Also in theory I am thinking only that once this hissing noise will be gone these codes will be gone too due to there’s a vacuum leak in the brake booster. I am not sure and asking for your wisdom on how to resolve this issue.

Thank you guys!

 

[whtbronco]

I agree it sounds like the brake booster is leaking. To test it carefully pull the vacuum hose off the booster and plug or cap the end of the hose with something that can't get sucked in. Then you can see if your lean symptoms clear. Do not drive with the vacuum hose removed from the booster. Your brakes will not work well due to having no power assist. You should also not hear the hissing anymore either.

 

[StibbyWonder]

I agree it sounds like the brake booster is leaking. To test it carefully pull the vacuum hose off the booster and plug or cap the end of the hose with something that can't get sucked in. Then you can see if your lean symptoms clear. Do not drive with the vacuum hose removed from the booster. Your brakes will not work well due to having no power assist. You should also not hear the hissing anymore either.

Ok bro I'll try this one out and I'll inform you right a way what will be the outcome. Thanks for your input.

 

[Gary Waugh]

My daughters Edge had the same hissing noise, it was the brake booster, bad news it cost $1000 to have it replaced by ford, I am too lazy to do it myself!! The part was about $800 and $300 for labor!! Not cheap, but the brakes now work very well!!

 

[StibbyWonder]

My daughters Edge had the same hissing noise, it was the brake booster, bad news it cost $1000 to have it replaced by ford, I am too lazy to do it myself!! The part was about $800 and $300 for labor!! Not cheap, but the brakes now work very well!!

That price is not cheap but I tried to look for alternative like after market part for this brake booster. Good that the brakes were ok already.