c928jon

Hi,

Firstly hello to all and apologies for being a newbie and crying out for help first post. 180000miles and i've just come across my first tricky fault.

I have a 1998 C class estate c200. Whilst braking gently there is a hissing noise and the pedal is drawn down and the car performs emergency braking, this is very scary especially with traffic behind you. There has been no warning light on at all, except three years ago when the brake pedal switch failed!

Has anyone experienced this before? After a quick read of the manual i'm guessing servo diaphragm sensing module but i'd love a second opinion just incase it's a vacuum leak or similar.

I'm glad it's an estate,plenty of crumple zone at the rear..JOKE>>it's not funny at all!

davis449

I would venture to say it's probably not a vaccum leak. That would most likely cause there to be less boost. I would say that the servo diaphram sensing module could be to blame. It probably has to be something that has to do with the controlling of the brake booster.

c928jon

Thanks for that, I think I agree, servo module. I know brake pedal switches are prone to failiure and wondered if that could cause this type of problem?