Brake servo restricted

[sorin s]

thank you KH904,

 

is it the one advised a few messages up? is it the MAP Brake booster pressure sensor?

 

 

[ian.f]

1 hour ago, sorin s said:

Hi all,

So glad I discovered this forum.

6 weeks ago, while reversing my 2016 A6 S line, my dashboard started to light like a Christmas tree, showing the following errors/faults:

- stabilisation control (ESC/ABS): fault!, see owners manual

- hold assist: unavailable

- main beam assist: system fault

- tire pressure: system fault!

- parking brake!

- Audi adaptive light: system fault!

- brake servo restricted. You can continue driving. Please contact workshop.

 

Since then, I probably did a further 500 miles and the car drives as normal...or at least I didn't feel anything suspicious with it; lights work ok, it brakes ok, steering wheel is ok, parking brake holds ok. 

 

Have any of you experienced similar? Do you have any advice?

Thank you.

 

I second, DO NOT DRIVE ANOTHER MILE! 
Yes, buy the sensor that’s listed in this thread and change it before you drive it again. I didn’t, and it cost me a fortune to replace & repair the subsequent damage. 

[kh904]

1 hour ago, sorin s said:

thank you KH904,

 

is it the one advised a few messages up? is it the MAP Brake booster pressure sensor?

 

It's the brake booster pressure sensor

 

[sorin s]

Thank you both for the valuable advice. Just ordered one from Amazon; will share my feedback after I fit it.

[P3N]

Good move Sorin.

i had the same message, drove 19 miles all the while the message only stated “ contact garage”. But my car totally failed. It cost me nearly £4k. I hadn’t found this forum 😩  Don’t move another inch until you have fitted the new part.  I now carry a spare in the car in case it goes again. 

[Peter Reville]

Bought new sensor from audi and tried to replace it myself. I was able to release the wiring clip but not able to release the clips at either side. Any advice?

[sorin s]

On 4/29/2025 at 9:31 AM, sorin s said:

Thank you both for the valuable advice. Just ordered one from Amazon; will share my feedback after I fit it.

Hi all,

2 weeks ago I bought the said sensor and installed it myself, however, the errors remained in the dashboard. Following that, I decided to take the car to a specialist and after they diagnosed it, it was found that the RHS front ABS speed sensor was faulty. After replacing it and running another diagnosis, it was found that the wiring loop for this ABS sensor was fried as well and that required to be replaced. In the end, it cost £ 525 to fix it. I attach the invoice to show the error codes, hopefully it will help others.

 

[kh904]

Ouch, that's made your wallet lighter. At least the ABS module wasn't bricked!

Any idea how the wiring loom got fried?

[sorin s]

What they said was that when the ABS sensor failed, the wiring loop got shorted... don't know what to say, I don't really trust garages/mechanics  🙂

[Forgot my password]

Thanks for the above responses.

I tried again to remove the sensor with the help of youtube videos. I was successful this time and was able to fit the new part myself. Fault message was removed automatically as suggested by the video and all is good. I did not have to get a diagnostic test. I understand Audi is aware of this common problem and have since modified the part. I hope this is of assistance to anyone having the same issue.

 

[Flatspell]

Hi, new to this forum. Would like to thank all the members as read about the lockout that occurs after about 20 times the warning appears.Replaced the sensor, cleared fault using vids and has never appeared  again.

110 pound from main “stealer” ,was quoted over 3 grand by an independent , thanks to this forum saved a small fortune and all the headaches.

When I mentioned the fix to the independent garage they looked at me blankly, didn’t know about it.
Thanks to all.

[kh904]

Glad to hear you got it sorted Flatspell.

To be fair, unless the garage specialise in Audi's, they may not know about this specific issue. They'll just replace the part that's likely to be the issue after a diagnosis scan.

 

[Jotenhiem]

Read the advice on the sensor bought one on Amazon replaced it after watching it on You Tube and it’s cured the issue

[Steve Q]

48 minutes ago, Jotenhiem said:

Read the advice on the sensor bought one on Amazon replaced it after watching it on You Tube and it’s cured the issue

Glad you got sorted 🙂

[Augh1234567]

Any advice would be appreciated. Having the error message "break servo restricted intermittently" and stop start being disabled but not every time I drive the car. No issues with breaks juddering etc. 

Bought pressure sensor and replaced it but on doing so the message is back each time the car starts. Moved off car for a small drive and on breaking the breaks started juddering so put back in the old sensor and now message is gone again and breaks feel normal. Any ideas as to if it's actually the sensor or is it likely to be some other issue like electrics, servo pump or the plug itself? 

[Jotenhiem]

I had the exact experience it started off with the message but it was was intermittent until the brakes started juddering. I joined the Audi club and seen the advice watched on you tube  how to change the sensor and it worked no issues since

[Augh1234567]

@Jotenhiem Was it an Audi part or from autofactors? I got this one from auto doc so maybe the issue lies there. 

[Jotenhiem]

56 minutes ago, Augh1234567 said:

@Jotenhiem Was it an Audi part or from autofactors? I got this one from auto doc so maybe the issue lies there. 

I got mine from Amazon 20£

[Jotenhiem]

 

 

[Flatspell]

Bought mine from main dealer after reading some people having issues with generic parts. Was expensive (100 plus) but worked first time. Did run vcds and erased any errors, so don't know if thats the reason it's been ok from then on.

[kh904]

I also bought mine from a main dealer, as I wasn't sure if I could trust a chinese copy (can save save £80 if it works, but could potentially lose £3k+ if it failed). 

By the sounds of most people's experiences, the generic parts seem to be ok

[ian.f]

@Jotenhiem when you have the errors on the dash, are they the yellow warning messages, or have you ever seen the red one? If you’ve seen the red one, then you’re probably past the point where replacing the sensor won’t solve the issue I’m afraid.

I let mine get to red warning and only then the brakes started juddering, so it sounds like the abs unit may have failed already, based on my experience  

If you haven’t seen any red warnings, then I wonder if the new part you’ve got is defective?

You could try buying a couple from eBay or somewhere else and see if that solves the issue?

If you haven’t seen the red, still do not drive it until replacing the sensor again. 
 

Good luck 🤞

Edited 2 hours ago by ian.f
Forgot info

[kh904]

27 minutes ago, ian.f said:

@Jotenhiem when you have the errors on the dash, are they the yellow warning messages, or have you ever seen the red one? If you’ve seen the red one, then you’re probably past the point where replacing the sensor won’t solve the issue I’m afraid.

I let mine get to red warning and only then the brakes started juddering, so it sounds like the abs unit may have failed already, based on my experience  

If you haven’t seen any red warnings, then I wonder if the new part you’ve got is defective?

You could try buying a couple from eBay or somewhere else and see if that solves the issue?

If you haven’t seen the red, still do not drive it until replacing the sensor again. 
 

Good luck 🤞

I agree, it could be a dodgy sensor.

 

If you do get the red warning light, the ABS unit will be bricked!!!

It will cost thousands of £'s to replace!

HOWEVER, the good news is that there are companies that can rese tthe unit at a fraction of the cost (still hundreds of £'s and you need a mechanic to remove the part so you can send it off).

Please see one of my posts earlier in the thread for one such company that offers this service (I have no affiliation)

[Jotenhiem]

There were no warning lights it was a message on the dash saying Brake servo but it is ok to drive but contact dealer.

[kh904]

11 minutes ago, Jotenhiem said:

There were no warning lights it was a message on the dash saying Brake servo but it is ok to drive but contact dealer.

Ignore the message that says it's 'OK to drive'!!!!!

The message is incorrect!!!

 

DO NOT DRIVE ANY FURTHER (try not to brake too hard and park up as as soon as possible where safe to do so).

Buy the required sensor and replace it asap.

Edited 7 minutes ago by kh904
added more info