Q: Brakes hiss when I use them

asked by on October 29, 2015

The ABS light has been on for a few weeks in my 2007 Camry V6 that I have driven for around 104,000 miles, and there's a hissing sound when I apply the brakes. I had my brakes and rotors changed last week by my mechanic friend, and I still was having the same issues. Today, the brakes lost power and it's like having old school manual brakes. Help, please.

Well, it sounds like you may have a vacuum leak coming from the brake booster. I definitely recommend you do not drive the vehicle until you have an independent mechanic look over it, as this is a major safety concern. Typically when you will hear a hissing sound from applying the brakes, or if you hear the sound but the hissing noise goes away when the brakes are applied, it is a very good indication that the diaphragm in the brake booster is failing. The diaphragm allows air to escape the system and thus makes it harder to apply the brake pedal when it is failing. In addition to this, a bad or failing brake booster can be a symptom of another hidden problem, which is known as a leaking master cylinder. Now these two issues don’t always go hand in hand, but they often can and a certified technician will be able to determine if the master cylinder is leaking by separating the master cylinder from the vacuum brake booster and inspecting the cavity in the vacuum brake booster for signs of brake fluid. Brake fluid can eat away at and break down the diaphragm inside the vacuum brake booster as well. Before a repair is attempted, a diagnostic scanner is used to communicate with the ABS computer to determine if the warning light is related to this primary concern. If it is the case, the diagnostic scanner is used to clear the code from the computer and you can have the power brake booster is replaced. If that is not the case, further diagnoses will be needed to identify the problem.

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