I have a 2014 A6 Avant and I'm getting a really strange power loss when driving that lasts for less than a second.... I could be in any gear and it's not just when accelerating, but if I am accelerating hard the power loss is much more noticeable - really jolts the car and throws you forward in your seat. To passengers it feels like I have dabbed the brakes. If it happens when I'm pulling away it feels like I have stalled but then the power comes back. It's like some kind of extreme mis-fire. This happens on average once a day.  

Another issue I have which might help diagnose the first problem (if they are related) is that I'm losing coolant but it's been into the garage and they say there is no apparent leak from the tests they've done and they have checked the oil for any milky-ness. I'm thinking maybe head-gasket but wouldn't I be seeing more regular symptoms and milky oil? Starting it seems a little rough and sluggish and very occasionally it doesn't turn over first time but have replaced the battery. Seems to run fine once started. I'm not sure what checks you do for a head gasket but pretty sure the garage looked into that.

I'm really hoping all these mystery problems are somehow related but have a feeling it is going to be expensive. If anyone can help with advice I would appreciate it. It's going back into the garage next week for another look but they seem to be scratching their heads too. 

Have you had a diagnostic check to see if any fault codes flag up? 

Could it be the turbo? 

If you're loosing coolant then it's got to be going somewhere. Could be a failing expansion tank cap. 

On 4/21/2023 at 9:23 AM, Toby73 said:

I have a 2014 A6 Avant and I'm getting a really strange power loss when driving that lasts for less than a second.... I could be in any gear and it's not just when accelerating, but if I am accelerating hard the power loss is much more noticeable - really jolts the car and throws you forward in your seat. To passengers it feels like I have dabbed the brakes. If it happens when I'm pulling away it feels like I have stalled but then the power comes back. It's like some kind of extreme mis-fire. This happens on average once a day.  

Another issue I have which might help diagnose the first problem (if they are related) is that I'm losing coolant but it's been into the garage and they say there is no apparent leak from the tests they've done and they have checked the oil for any milky-ness. I'm thinking maybe head-gasket but wouldn't I be seeing more regular symptoms and milky oil? Starting it seems a little rough and sluggish and very occasionally it doesn't turn over first time but have replaced the battery. Seems to run fine once started. I'm not sure what checks you do for a head gasket but pretty sure the garage looked into that.

I'm really hoping all these mystery problems are somehow related but have a feeling it is going to be expensive. If anyone can help with advice I would appreciate it. It's going back into the garage next week for another look but they seem to be scratching their heads too. 

Hi head gaskets do not always put water in to the oil it is more the other way where gas is introduced in to the cooling system and via the exhaust gas escape water can get back the other way in to a cylinder, ask the garage to do a sniff test on the header tank, this involves !Removed! an adapter with a reservoir of the testing fluid to the expansion tank then run idle for 20 mins, the fluid will change colour if it detects exhaust gas, I agree with Steve a full scan is your best route.

Steve.

Many thanks Steve 1 and Steve 2! Sorry I have only just seen these responses - it's in the garage today so I forwarded your comments in case it helps them. Waiting for the dreaded phone call! Will post an update if there is anything interesting to report

Hello Toby,

How much coolant is it losing over say 200 miles or per week? 
Kind regards,

Gareth. 

Hi toby, did you get a solution to your fault? Sorry to dig up an old post 

Hi Davie,

No I never got to the bottom of it. I still have the car but it has been off the road since June last year - I keep meaning to get round to fixing it so I can sell it. Someone recently gave me the name of a garage fairly local to me who are Audi wizards apparently so I keep meaning to take it over there. I see that you have exactly the same issue - I will update you if they manage to find the cause but if you work it out first I'd really appreciate you letting me know what it was. 

Good luck with yours!

Hi toby, 

thanks for the reply, i certainly will let you know if i find anything.

cheers, Davie 

Did you work out what it was Davie?

Hi toby, sorry for the late reply, turned out to be a faulty crank sensor. Unbelievable how it never once threw a fault code. I changed it at the end of last week and it’s been fine ever since. Pig of a thing to change. Well I say that could probably do one in about 20 minutes now. Easy once you’ve done it. 
 

if your going to change yours my top tip is don’t try and unplug the sensor, remove the bolt and take the sensor out with it still plugged in. Fit the new one and then plug it in. An inspection camera helps, luckily I have one. 

That’s awesome. Tempted to come to you to have it done. You run a garage right? Only an hour away. Possible?

I’m in Wick in Caithness. Where are you? 
 

im sure I could fit it for you no problem. If your willing to travel 👍

Hi Toby. 
 

Are you just outside London? If so it’s at least a 12 hour journey to where I am. 😳

Haha - different Wick then! 

Yeah unfortunately mate. Hope you get it sorted 

Davie, just to let you know I had the crank sensor replaced and it worked! Have been driving it for over a week and no more issues. Thanks so much - my garage saw nothing in the diagnostics and were suggesting they start ripping out all the wiring estimating up to £2k with no guarantee of finding the cause. 

Hope this thread helps someone else.

Hi Toby,

that’s great news! It’s certainly a strange one and to be perfectly honest if my car had came into my garage I wouldn’t have gotten to the bottom of it I don’t think. I would have told my customer to take it to Audi. The only reason I persevered for so long was because it’s my own. Would have been so easy to load the parts cannon and take aim but I don’t do that if I can help it. 
 

just for future reference I’d have fixed it for you for £1500 😂

Glad I could help and hopefully more people see this post and it helps them too. 
 

take care 

Davie 👍

Fantastic result guys. Thsnks for keeping this one updated. 
hopefully it will help somebody in the future

On 4/19/2025 at 5:45 PM, Autoquip said:

Hi toby, sorry for the late reply, turned out to be a faulty crank sensor. Unbelievable how it never once threw a fault code. I changed it at the end of last week and it’s been fine ever since. Pig of a thing to change. Well I say that could probably do one in about 20 minutes now. Easy once you’ve done it. 
 

if your going to change yours my top tip is don’t try and unplug the sensor, remove the bolt and take the sensor out with it still plugged in. Fit the new one and then plug it in. An inspection camera helps, luckily I have one. 

Hi, my 2014 audi a6 c7 2.0 tdi ultra develop exactly same fault. Could you please explain where crankshaft sensor is located and what's best way to change it please? 

Many thanks 

Hi dani19 sorry I’m not great with these forums. 
 

you can get it from the top, I had to use an inspection camera to help locate it. It’s on the passenger side of the engine and it points into the flywheel. Best way I found was to take the sensor out with the plug still attached as I couldn’t get in to unplug it,  the bolt is captive in the sensor I’m sure. Then once it’s out plug the new sensor in and feed it back in and tighten the bolt. Might make life a little easier if you remove the header tank but I managed without removing it. 
 

let me know how you get on 👍

Many thanks, sensor arrived today so will try to get it done this weekend. 

My car had 155k millage  when this happened for the first time, just curious what was yours?

Best regards 

Daniel 

Edited November 7, 2025Nov 7 by Dani19