2016 (66) A4 Avant 2.0 38k miles Engine management came on a couple of weeks ago, then went out. Bought a code reader and it was indicating P20C4 which is a reductant heater circuit high. Came back again week later then went out. Had the 2000 mile adblue warning earlier in the week and then on my 200 mile journey today went to 1300 then I got a "adblue fault...650 miles until no restart". restarted the car and it went back to 1300 miles again! I've just plugged the code reader in again and it is firing up P20E8 and P20FE which are related to pressure. My car is spitting out a lot of spurious ****. Has anybody experienced any issues and if so was it costly?