I would stop plugging the code scanner in as will drive you mad ! (-: … a bit like googling and scaring yourself every time you have a pain. I played with one on my old C class and it always found an error code on something, but car was totally reliable and never displayed the dash light.

My current 2018 GLC220d (80k miles) always comes out of the Merc service showing a full Adblue tank and a range of 12000ml. And 12000mls later it always shows <> 1/2 tank and 6000mls remaining. I don’t even look at it between services now as car will warn if getting low.
The relationship between the tank level and mileage display isn’t fixed as Adblue usage varies according to how the engine is used. Mileage is just a running estimate of expected usage - same as the “fuel range” mileage display.
I’ve read many times that it is unwise to keep topping-up the adblue tank as it confuses the system, is best to run it down to 1/4 tank then fill and reset system.

 

Thanks for your thoughts and yes I won't be plugging the scanner in all the time. It was just initially to try and see if there was anything that might benefit from investigation.

I can understand that the adblue usage will depend on how the engine is used and how the ecu tries to mitigate the emissions. I was going to try and keep the adblue tank no more than half, and because it was showing 1/4, that's why I tried to top it up. Never my intention to keep messing with it. However, currently its still showing as a 1/4 on the gauge but from my attempts to top it up actually pretty much full.

I'll message Topdon and ask them to confirm what exactly their adblue reset function is designed to do as don't want to screw something up. Don't really want to have to put it into Mercedes as that could be pretty expensive but equally I am not going to have the adblue system deleted which seems to be the solution a few people like to suggest.

I'll have a word with my regular garage and see what they think and if they can sort it.

 

Hi

Some background first to hopefully set the scene...

We recently bought, from a member of the family, a 2017 220d. Before we bought it I did a scan with a basic OBD tool(since then I've got a Topdon Topscan). Also took it to the local garage that we use for all our car servicing and they ran their Snapon tool on it and also gave it the once over.

They did get quite a few error codes, and I'd seen an engine management light warning, and the scan code came back as P229E circuit malfunction on a NoX sensor. One of the other errors was P0562 system voltage low. It's the original battery so figured that it was probably on the way out.

Now we know the cars history, and were being offered it for for a good price, so we'd sort of decided as long as there was nothing else major when the garage checked it over we'd factor in that we might need to spend some money sorting out any problems with the NoX/adblue system as there's plenty of posts about issues that can occur.

So after we bought it I put in a new battery and did a battery reset and cleared all the codes. Since then we've not seen any engine management lights or further error messages coming up. The only two I consistently get when I scan it with the Topscan is one to do with the left hand headlight and the other something on one of the rear doors. Neither item appears to have a problem.

Anyway to get to the adblue problem the dash display has shown it as about a 1/4 full and a range of 6500 miles and that hasn't changed since we bought it and we've done about 1200 miles. We don't do a massive mileage, and before anyone comments we know that isn't going to be ideal for a diesel, but we do have another car that's petrol and will keep an eye on our trips to ensure we don't do lots of short journeys. When we first got it I put in a bottle of Wynns crystal clean and protect as I'd read about problems with adblue crystalising and the brother in law couldn't remember when he'd last put adblue in anyway.

About a month ago I decided, as the range didn't seem to be changing or the level going down although we'd done a few miles, to try putting some adblue in. When I went to top it up from a 5l container, I managed to get about 2 1/2l in before it appeared to be full. Monitored the gauge over that month and still nothing changed on the display. The other day I decided to see if it would take some more and managed to get about another 1l in before it was to the top of the filler again. So I'm guessing it's using it and I can smell the slightly acrid stink that now seems normal around diesel exhausts which I guess is from the adblue being injected into the exhaust? We've not seen any messages about it not starting in x miles and no engine management lights.

So has anyone come across anything similar and any ideas if an adblue reset, which is a function available on the Topscan, might do any good and reset the system or are we looking at a big bill for a new tank etc? The local garage we use isn't into just firing the parts cannon at problems so would probably have a look and maybe empty and drop the adblue tank and see if there's anything that can be checked and/or cleaned.

Thanks for any thoughts.

Yes a filled mine to the brim , which I’ve since found is not the correct thing to do . It registered 7200 miles range for about 3000 miles before range started to go down.
I am lead to believe the best way of topping up is to not fill until the reading is just above 1/4 full and then top up to 3/4. This prevents add blue being in the tank to long, allowing it to crystallise.