Total brake faliue garage cant find problem!

[burtoni uk]

hello guys. i have just had a major problem with mr brakes on my 2003 audi a4 tdi 130 i have been having an issue with my brake pedals going hard and after this happening for 2 days it has now gone totally solid.. (as if keys out of ignition and pumping the break till hard)
i have rushed it striaght to mygarage that does my works fleet cars and after spending all day on it today he has no idea of the fault.
the car is in limp mode now permanantly the fault codes all relate to brake sensor but they have been wiped and not come back on.
after asking a few tech minded people they belive i may need to bleed my brakes as air may have got in somehow .
now the mechanic i spoke to today has told me the vacuum pump is working fine so cant be that and he doubts its the servo so im at abit of a loss.

sorry for the long post. thankyou in advance

[STEWY L]

hard pedal is usually the servo, i'm not sure if the A4 has the same problems
with water / plenum chambers causing servo to stick,
regards,
stewy.

[burtoni uk]

the mechanic at the garage said that he isnt anywhere near sure enough its the servo to go ahead with the work and find out that it isnt the servo. are there any ways to prove that it definatly is/isnt?
also rought how much do these braking servs cost?

[zollaf]

the vacuum pump supplies the vacuum. a pipe connects to the servo. the servo helps you brake. if the vac pump is pulling a vacuum and the pipe isnt split or otherwise leaking, then logic points at the servo. although you do say it drops into limp home mode, so attention should be paid to all the vacuum pipes, as these control the turbo, and a split here would affect that, as well as letting air in and loosing vacuum to the brakes.

[burtoni uk]

ok. thats makes alot of sense. so for a total novice in car anatomy.
audi a4 brake problems 101 says these pipes are located where?

[zollaf]

the main vacuum pipe comes off the tandem pump at the back of the engine, and connects to the servo. this is the thick pipe (1/2 inch or so). this is also then connected to smaller fabric covered vacuum pipes (1/4 inch approx) that run all over the engine bay. basically follow all the smaller pipes. a leak in any of these could cause your fault. have you also checked the plenum chamber where the battery and servo sit for water build up ? this can cause failure of the servo, due to blocked drain plugs then allowing water into the servo.

[burtoni uk]

ok so i need to check these hoses? however the mechanic at the garage said he check all the main brake hoses and even took them out and made sure they were clear... its all a confusing matter that he cant seem to help and i begrudge letting audi charge me £95 just to tell whats up with it