Adblue Fault P20E8 & P208C

[Cb1992]

Hello,

As per above, my 2017 A4 2.0tdi has the dreaded adblue fault. This has been an intermittent that usually cleared on its own but now seems to be a hard fault and down to last 100 miles before ‘no restart’.

I know this topic is very tedious with many posts on the web, but looking to gather my thoughts and ask few questions in my quest to fault find this error. To my knowledge it can either be;

1) Stuck adblue tank float/level sensor

2) Faulty adblue pump

3) Faulty control module (possible corrosion)

4) adblue injector clogged/broken

5) low/weak car battery *not seen much on this but have seen mentioned.

So far I have checked the injector looked very clean but nothing was passing through it when engine on,I then pulled the adblue line to injector, and again no adblue being pumped. Should be noted that my car battery is definitely on its way out to point stop/start not working and stuttering to start at times.

So this is suggesting a potential control module or pump fault. The question i have is would the pumping system be inhibited if level sensor is potentially stuck at empty or low level? Like a pump protection of sorts? And thus low pressure. And also, has anyone successfully fitted a used/second hand adblue control module to their car? Feel free to add any other checks I should carry out.

Car is on 124k miles and full service history by Audi. Got a baby on way so was going to be very soon parting ways with car, so reluctant to just fling £1200+ at full new adblue tank/pump system if it can be avoided. If I find any solutions in the meantime time I will post update on here. 
 

Thanks

[cliffcoggin]

I have no personal experience, but from what I have read the problem is caused by crystallisation. That being so it should be possible to flush the system with water to dissolve the urea.