when I step on the brakes it sounds like there is air coming out what does that on 2001 Volvo V70 XC

it happens everytime I get in the car and back out to the main rd but after driving for about 5 mins the sound goes away

Asked by for the 2001 Volvo V70 XC
2 answers
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THIS IS CAUSED BY THE BRAKE BOOSTER HAVING AN INTERNAL DIAPHRAM VACUME LEAK. CAUSING BRAKE BOOSTER VACUME PRESSURE TO ESCAPE WITCH CAN BE HEARD JUST OBOVE BRAKE PEDAL. .