what is causing hissing from brake pedel of volvo s80?
driving along there is a hissing coming from brake pedal when my foot is not on the pedal when i put my foot on the brake pedal the hissing stops the car is an automatic volvo s80
u have a malfunctioning brake servo.ign off,press brake pedal several times then hold down,start car while u maintain pressure.the pedal should suddenly go down,if not suspect servo or vacum connectuons
