Car hissing when let off brake

[alcgraham]

I have a 2004 Eddie Bauer edition. It just started this hissing sound when you let off the brake. It is driving fine. We do need to replace the rotors on the front but otherwise it is driving fine. I saw something about it possibly being a brake booster? Any guidance would be great.

 

[Hamfisted]

Do you have Traction Control with Advance Trac ? I recommend the Motorcraft unit.

Power Brake Boosters at Rock Auto

 

[alcgraham]

Thanks. I am wondering if it could be the hose. If I grab the accordion like boot next to the firewall the hissing stops. The brake pedal tests are all good. No pedal problems. So does that seem like the booster or just the hose.

 

[cattlecar]

Not the hose. The booster works by keeping constant vac on front of diaphragm and a regulator valve on backside where pushrod goes in throttles air entering back of booster to reduce vacuum so the diaphragm and master cylinder pushrod go forward to apply brakes along with your foot pressure. When the regulator fails it leaks vacuum. The boot has a foam silencer in it. When you touch boot you are affecting the regulator. It will need a booster or one day it may leak worse and drag your brakes while driving and then you'll need calipers, pads, rotors, and a booster.

 

[alcgraham]

Thanks for the input. We need to do a brake and rotor change anyway so that will be added to the mix. I appreciate the help!

 

[alcgraham]

Ok so we got the booster and my husband got it changed out tonight. It was the Duralast from Auto Zone for the Electronic Stability Control. However, now the car says check Advance Trac. How do we make this go away and why is it giving that error?

 

[Hamfisted]

Those rebuilt units from AutoZone sometimes have bad sensors right out of the box. You can try swapping out the sensor from your original one first. Do you have a code reader that will read chassis DTC codes ? Or a laptop you can install the free ForScan app on and read the codes?

 

[alcgraham]

Where is the sensor located? What does it look like? I don't have a code scanner. How do you scan from a laptop? I was planning on taking it to AutoZone to have them take care of it since it is their part that doesn't work correctly. Will we have to uninstall and reinstall it?

 

[Hamfisted]

Where is the sensor located? What does it look like? I don't have a code scanner. How do you scan from a laptop? I was planning on taking it to AutoZone to have them take care of it since it is their part that doesn't work correctly. Will we have to uninstall and reinstall it?

The sensor is on the brake booster right next to the master cylinder. You would've plugged a harness into it.

 

[alcgraham]

Great thank you!