Hi. Sorry, I’ve only just seen this post.
If you can find a C350 petrol with the M276 engine you’ll be doing well. They’re few and far between. Good luck. I bought mine new in 2012 and still have it because I can’t find anything better (in my price range!)
Yes, there are many problems with the NOx sensors, as there are with lots of petrol and diesel C-classes as well as several other Mercedes. But I think I may have found a work around - or ‘hack’ as the media love to call just about everything.
As far as I’m aware there are two NOx sensors. That’s been how many Mercedes have replaced on the three occasions I’ve let the loose. The first time was under warranty when the car was 10 months old. Second time when the car was just out of warranty but done free. Third time was when 6.5 years old. After lots of discussions with MB I managed to get them to contribute £1,000 to the replacement cost.
The next time the EML shone out (about 18 months later) I bought a cheap OBD-II reader. It showed two fault codes and I cleared them. They came up again a few days later, so I cleared them again. Not wanting to continue with this nor fight with MBUK to try to get them to pay again, I looked for someone who could delete codes permanently. By the time I’d found a remapper who claimed to be able to do it, one of the codes had appeared again.
The remapper was able to permanently delete the code that was active (P2214) but I couldn’t remember what the other one was so there was nothing he could do about it.
Everything was fine after that for very many months, but then I was reminded of that other code (P2218). I wasn’t able to get to the remapper I’d used before so I just cleared the code while I looked for somewhere closer. After a few days I had to clear the code again, but it only took a couple of minutes so no hardship.
Weeks went by and the EML didn’t come on again. Then months.
About a year later, up popped fault code P2218 which I cleared. Rinse and repeat a few days later. Then all good for another year.
This is what I’ve done since. About 5 minutes a year clearing the code for a supposed NOx sensor heater failure is less hassle and vastly cheaper than replacing the darn things.
My theory is that the ECU software has the boundaries set too tight for the permissible range of the sensors. They only have to creep out of limits briefly and the inflexible algorithm sets off alarms and declares that the sensor is faulty. Once the computer says no, it can’t go back. So even though that errant speck of contaminant has been blown away, “das sensor ist kaput”.
My car is mainly used for short journeys so doesn’t get enough good blasts to keep everything clear. I’m happy enough to tell the ECU once a year that it’s talking nonsense.
My recommendation would be to spend £25 on a reader so you can note and then clear NOx sensor codes over a period of time. Then get them deleted permanently. Even when flagged up as faulty, the NOx levels of a petrol engine are way below those of a diesel so we’re not killing anyone. It’s probably illegal, but who’s going to know? Especially since everything is probably still working fine anyhow. I still have my car serviced and MOTd by Mercedes and they haven’t flagged up any issues.
