Urgent help with AdBlue fault on A6 C8 40TDI

[A6 Avant]

So I recently had an issue with an Exhaust Gas Temperature Sensor causing an error (Bank 1 Sensor 3). Got a replacement from Audi and changed the sensor and that seems to have resolved that issue. However, something that's been done during the process of replacing this sensor seems to have prompted a different error: "AdBlue/DEF fault. No restart in 650 miles."

First thing I tried was topping up the adblue, clearing the fault and going for a drive. It seemed to clear and I drove for the rest of the day thinking it was sorted. But then when I turned the car on the next morning the error appeared again and I now it won't go away (the fault won't clear).

I've been trawling the internet for an explanation and it seems like quite a common issue with VAG cars. From what I've seen the main solutions have been:

1) A reset/recalibration of the adblue metering system - apparently it can go 'out of whack' after work has been done on the system (Can i do this with OBDeleven?)

2) A software update is required - which seems odd on a 5 year old car but apparently that's fixed it for some people

3) Replacement AdBlue tank/sensor unit at a cost of several hundred pounds just for the part (so I'm hoping it's not this) and it would be a bit random if it's suddenly failed at the same time this job was being done.

4) A couple of people have said they had a faulty Nox sensor or the AdBlue injector needed cleaning/replacing but these issues seem to be less common.

We're due to be going away on a family holiday in the car shortly and I've currently got a 600 mile countdown before the car won't turn on so I'm feeling really stressed about it. Just wondering if anyone can offer any help/advice/experiences to point me in the right direction please as I'm pretty sure Audi won't even book me in before we're supposed to be going away?

 

[Sibmets]

Better to scan for fault codes before start guessing all the possible solutions.
My adblue fault was sorted by changing the Adblue controle module, I had a fault:

P21CA00 - Reductant Control Module Supply Voltage Circuit static

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[A6 Avant]

Better to scan for fault codes before start guessing all the possible solutions.
My adblue fault was sorted by changing the Adblue controle module, I had a fault:

P21CA00 - Reductant Control Module Supply Voltage Circuit static

Sent from my Pixel 6a using Tapatalk

Thanks for your reply. Sorry I should have mentioned that I have also been scanning with OBDeleven and got the following errors:

* Originally only got P242A error which was the EGT sensor bank 1 sensor 3 which we changed and that error went.

* After doing that the AdBlue/DEF fault: no start in 650 miles appeared with fault codes P208B (reductant pump A control range/performance) and P2BAF (NOX system driver inducement active).

 

[A6 Avant]

UPDATE: I went to Audi earlier to see if they could 'reset the AdBlue metering system' as this has apparently fixed the problem for others with the same issue.

They said the reset wouldn't work in this instance because one of the errors is a static fault. They quickly plugged it in and, based on the fault codes, said they thought the AdBlue pump needs replacing. It turns out this is even more expensive than I thought at around £1500 just for the part from Audi (it's only available as a complete unit so you have to replace the entire tank with the pump).

So my options seem to be to pay £1500 + labour to replace the pump/tank (which is an insane amount of money for a completely non-essential part) or my mechanic friend has suggested an 'AdBlue delete' which is apparently becoming more and more popular given all of the problems people have with these systems and the incredibly high cost of maintaining them.

I've also looked at picking up a second hand AdBlue pump but they all seem to have slightly different part numbers (same number but different letter at the end) so it's hard to know if it would be compatible or not? Currently on 550 miles remaining and we can't go on holiday until it's sorted so if anyone has any advice (or any experience of getting an Audi AdBlue system deleted) then that would be extremely helpful.

 

[PaulR7]

I've never done an adblue delete myself but I can answer in regards to the part number, as long as the letter is further down in the alphabet compared to what you have fitted right now then it won't be a problem changing over to it as all it means is just a later revision of the part and works as a direct plug & play replacement.

 

[elan2s]

AdBlue delete (if detected) could result in an MOT failure as the emissions parts of the car are meant to be to the same spec as they left the factory and this would not be the case.

 

[Adrian1871]

well i had this issue before turns out they changed adblue tank/sensor waited 4weeks car got returned fault reappeared within 1000miles car went back waited 3months and had a brand new loaner turns out its the adblue ecu! they are a common fault,the back order as the ecu needs changing new supplier old abdlue ecu corrodes major problem with adblue systems must have cost audi well there supplier whom im aware has been changed ! internet states they corrode due too casing flaw theres a pin hole which corrodes with damp due too flawed design hence new supplier. i even received a cheque for £450 due too this issue

 

[A6 Avant]

well i had this issue before turns out they changed adblue tank/sensor waited 4weeks car got returned fault reappeared within 1000miles car went back waited 3months and had a brand new loaner turns out its the adblue ecu! they are a common fault,the back order as the ecu needs changing new supplier old abdlue ecu corrodes major problem with adblue systems must have cost audi well there supplier whom im aware has been changed ! internet states they corrode due too casing flaw theres a pin hole which corrodes with damp due too flawed design hence new supplier. i even received a cheque for £450 due too this issue

Interesting, presumably this was all under warranty?

Do you reckon the whole problem was ultimately caused by the ECU fault all along and the pump/tank (which comes as one unit) were not faulty?

Or do you think the pump/tank were faulty and then the ECU subsequently went as well?

 

[A6 Avant]

I've never done an adblue delete myself but I can answer in regards to the part number, as long as the letter is further down in the alphabet compared to what you have fitted right now then it won't be a problem changing over to it as all it means is just a later revision of the part and works as a direct plug & play replacement.

Thanks that’s really useful to know about the part numbers.

 

[Adrian1871]

yes as i took it in first time they diagnosed pump sender unit complete apparently cannot be separated but i know parts manager well he said all that was replaced was sensor so on second visit with same issue same fault no start in xxx miles she rang me up saying same part needs replacing i said this cannot be possible ive waited a month now im being told 3 months wait!! turns out they have changed supplier of adblue ecu ! and thats why the delay was so long !

 

[Adrian1871]

ecu all the way!

 

[Adrian1871]

funnly enough looking at my new car today the app says 1500 miles refill adblue! no light warning on dash,says on app with milage fuel and oil level 1500miles so why no warning light? service shows new ablue injector fitted this year? popped bonnet and there she was new adblue injector lol theres a fuse or resistor attached too it ???? im wondering if this sytems working as ive done 2k with adblue level not moving an inch still says 1500 miles on app milage gone up and fuel level goes down so im curios?

 

[Sibmets]

funnly enough looking at my new car today the app says 1500 miles refill adblue! no light warning on dash,says on app with milage fuel and oil level 1500miles so why no warning light? service shows new ablue injector fitted this year? popped bonnet and there she was new adblue injector lol theres a fuse or resistor attached too it ???? im wondering if this sytems working as ive done 2k with adblue level not moving an inch still says 1500 miles on app milage gone up and fuel level goes down so im curios?

It usually says ">1500 miles" - no? Maybe You just missed the ">" sign?
The number is not gonna decrease unless you get less than 1500 miles remaining, while itnis above that, it will not show an actual number, than can only be seen using proper scan tool.

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[elan2s]

Think you only get the alert on the dash telling to you top up the adblue when it drops below 1000km/650 miles

 

[Adrian1871]

1500 miles the alert is set at so im wondering why im not getting an alert or using any adblue i have vcds anyone know correct measuring block too see actual adblue level? Thanks Sibmets yes i doo have that arrow so im above 1500 miles? i get it now

 

[Adrian1871]

 

[Adrian1871]

i had the 650 miles remanning when mine was faulty!!! it should say 1500 when alert initially indicates an alert on cockpit!