Hello,

I am wondering if anyone else has had this problem. The adblue is fully topped up but I get a warning saying "error no start authorised in 650 miles" or something 20650 miles or sometimes not at all. For a little while the orange "check engine" warning light was on and the code (po204b)said that the reductant sensor needed replacing but now that light is no longer on. I am also getting an intermittent warning light saying my rear light is out (which is isn't). That issue seems to be after the boot gate is slammed shut.

My suspicion is that there is some wiring issue. VW wants to charge me a grand to replace the sensor but I am not convinced that is the problem (and I don't have a grand to pay them). I am trying to decide on my next steps. I am debating:
1. Replacing the Adblue sensor myself
2. Checking fuses
3. Trying to find a wiring problem (but I don't know where to begin)

Any help would be much appreciated.

That code you have mentioned (po204b) could that possibly be P0204? if so you either have a wiring fault to number 4 injector or a faulty injector.