I've put a new sensor on and problem still there.      How serious could this be?  It's now booked into my Audi garage for a diagnostic.  

Keep us posted on how you get on. Stop/start issue could be caused by a failing battery. 

Could the replacement sensor be faulty? 

It's only just (3 weeks ago) had a service and MOT.   Nothing picked up then.      I'll see what happens on Tuesday.  Diagnostic is going to cost £150 before anything else.  No choice really now than to go ahead with this.    Many thanks Steve Q

See this 

https://www.audiownersclub.com/forums/topic/13415-brake-servo-restricted/#comment-47826

 

Thank you cliffcoggin.  Lots to read on that forum.    I have read about the warnings on other forums which lead me to buying a sensor and having a go myself.  The company I bought from:   "partsforgermancars" has been mentioned here a few times.  Perhaps the switch is faulty but we have no way of finding out.  

Even the Audi part is reputed to be unreliable so it's possible your new one is faulty, in which case it would be unwise to drive the car until it goes to a garage. However I think it is more likely to be a failing battery as Steve Q mentioned because of the stop/start fault.

Let's hope the diagnosis shows something.

Keep us posted on how you get on. Definitely don't drive it unless you really have to as long term it can damage the abs pump/module which is a big bill. 

@Steve Q  will do. Asked for a call tomorrow morning stating my worry about ABS.

Thankfully I’ve not long to wait for the diagnosis / Tuesday.

 

Hi all. Thanks for the advice about the fault. 
Back from Audi garage. Fault found with replacement switch I bought. They’ve done a diagnostic check and fitted  new one. All OK now. 

Glad to hear it.

On 7/8/2025 at 5:13 PM, Pauline S.S. said:

Hi all. Thanks for the advice about the fault. 
Back from Audi garage. Fault found with replacement switch I bought. They’ve done a diagnostic check and fitted  new one. All OK now. 

Glad you got sorted 🙂

Hi ive had the same problem. Replaced the sensor then had to replace the abs module. Got it repaired and replaced today. The ABS codes cleared but the brake servo restricted came back.

Went and bought new pressure sensor and the brake servo restricted is still on the dash and the brakes are also faulty. 

Unsure what to do. The 1st pressure sensor worked but then I had to replace the ABS MODULE and once replaced the servo fault came back. 

Both pressure sensors I bought are zmetzger 5Q0906207B cost £62 each. Bought both from a local supplier. Ive been told that audi have done away with the B codes at the end and to get an original but im unsure as ive read loads have also used the B code ones fine. Any help would be much appreciated 

 

Edited October 18, 2025Oct 18 by Paulag