Skip the auto shop - Our mechanics make house calls

Q: I hear a hissing sound when driving, and it only stops right after applying the brake pedal.

asked by on

I would just like to know the problem, and if I have to replace any parts. Thank you.
My car has an automatic transmission.

A: A likely cause of the hissing sound is a le...

A likely cause of the hissing sound is a leak in the atmospheric valve within the power brake booster. The reason the sound ceases when you apply the brakes is because the vacuum valve within the booster closes upon pedal application, thus cutting off the air flow into the booster through the atmospheric valve where the hissing noise is being generated. If indeed this is diagnosed as the cause, in an examination by YourMechanic, the recommended fix would be to replace the brake booster. However, other sources of vacuum leaks would have to be ruled out as well. If you desire this to be inspected by YourMechanic, please fee free to follow up and request a hissing noise at brake pedal diagnostic.

Was this answer helpful?

Need advice from certified mechanic? Get help now!

Over 1000 mechanics are ready to answer your question.
The statements expressed above are only for informational purposes and should be independently verified. Please see our terms of service for more details

Get an instant quote for your car

Our certified mechanics come to you ・Backed by 12-month, 12,000-mile guarantee・Save up to 30%

Get a quote

What others are asking

Q: Engine knock in 1999 Chevy S-10

Sad but true--those things had the engine problems from the get-go. There used to be a website where people had class action suits for this car. They were suing GM, but I’ve noticed lately that the website's gone. I don't...

Q: My transmission is "clunking"

Sometimes a transmission is serviced when it is on the border of starting a problem. This will cause the transmission problem to show itself in a short time. The new fluid will clean out areas of wear, and the thicker...

Q: My rpo code is m30 which means I have a 4l60e, what is the difference between ID code LAD and CAD will they interchange?

Hello, the transmission will bolt up to vehicle. The difference can be configuration of operating pressures, clutch pack stack and shift points. These codes are for engine and vehicle type match. The transmission will work just may not have smooth...

Related articles

How Long Does a Heater Control Valve Last?
Keeping the right amount of coolant in a car is essential in keeping the engine at the right temperature. Failing to have the right amount of coolant or even bad elements...
How to Renew Your Car Registration in Oklahoma(DELETED)
Having your car registered with the Oklahoma Tax Commission is an important part of driving legally in this state. You will need to do this within 30 days of moving to Oklahoma...
P2103 OBD-II Trouble Code: Throttle Actuator Control Motor Circuit High
P2103 means there is a fault with the throttle actuator control motor circuit, likely due to a defective electrical component or part.