Hissing noise coming from brakes


Registered User
Wondering if anyone has experienced this issue...basically there is a slight hissing noise coming from the brake pedal area but when I depress the pedal it stops. I discovered it last year some time (when radio & air-con were switched off) and initially it worried the hell out of me, but I don't believe there is anything amiss with braking performance. I had it checked out at APS in Brackley when it was last serviced but they weren't able to identify any fault (they did mention something about a valve that may be the cause?).

Have trawled the net searching for the same issue and it seems other VWs & Audis have had the same symptoms but there's no definitive solution. Is it worth going back to the stealers to get it looked at while still under warranty or will they just rip me off? :-O


(2009 Audi S3 Sportback)


Registered User
VCDS Map User
Gold Supporter
Check your servo as follows;

With the engine switched off, pump the brake pedal until it goes very firm (about 5 or 6 times is enough). On the last down stroke, hold the pedal there whilst you start the car. The pedal should now drop markedly as the Servo assist function operates. When the pedal stops moving keep holding it and now switch the engine off. Keep holding the pedal down for about 20 seconds, there should be no further creep. Now release the pedal and pump it again. You should get at least three clear servo assisited pumps before it goes frim again. If all this checks out then the servo is ok. If not, you may have a leak in the servo system and that is the hiss you can hear.

Hope you can follow that and it helps.


Registered User
Thanks for the clear instructions Gary. Just gone to car park to test and all seems ok with the servo. It's interesting that when the pedal was pumped the 2nd time and went firm there was no hiss when released, until the engine was started - the pedal stayed firm.


Registered User
Mine did this before to the previous owner and Awesome GTI did a repair to stop it, I now have the noise back and have found it seems to be coming from a brake vac line. I will try and take some pics so you can jiggle it to see if it shuts up lol


Registered User
my car brakes have recently gone quite stiff and dont stop as quick as they used to, when i push my brakes down it probably goes half way down and then literally stops. i can hear a hiss every time i push the pedal down, does anyone know what it could be?

A3 1.9tdi 55 plate