Nox sensor

[JuannyH]

Hi all. I have my engine management light coming on every now and then . I bought a reader to turn it off and find the fault. It tells me it’s a Nox sensor heater problem. Phoning Mercedes, I was told they had no idea when or if they were getting any more Nox sensors in! It was “out of their hands”. So really helpful. It’s a 2015 car. The thing is it can go one day without the warning going back on or even 6 weeks. I was told the part number by Mercedes and bought a sensor from a business on eBay with good reviews. I’m worried that swapping over the sensor MAY open a can of expensive worms. I’m stuck as to what I should do… any ideas?

 

[TC350]

Hi all. I have my engine management light coming on every now and then . I bought a reader to turn it off and find the fault. It tells me it’s a Nox sensor heater problem. Phoning Mercedes, I was told they had no idea when or if they were getting any more Nox sensors in! It was “out of their hands”. So really helpful. It’s a 2015 car. The thing is it can go one day without the warning going back on or even 6 weeks. I was told the part number by Mercedes and bought a sensor from a business on eBay with good reviews. I’m worried that swapping over the sensor MAY open a can of expensive worms. I’m stuck as to what I should do… any ideas?

I can only comment that I’ve had the same issue - the fault code reappearing after different time periods. Those varying time periods roughly align with different usage: just short trips and it’s back on within a week; a couple of long trips and it’s over a month to reappear.

My conclusion is that it’s not faulty sensors, but instead tight limits on the accepted range in the software. The short trips clogging up the sensitive sensors quicker, then cleared during a long trip.

I‘ve persisted with cancelling the warning with my reader, and after a few repeats the EML stays off for a year or so. Then it’s repeat. It only takes a couple of minutes to do the cancelling, so it’s no big deal. It’s a lot easier and vastly cheaper than replacing sensors.

My recommendation, for what it’s worth, is to give the car an “Italian tune up” (a good blast) to clear everything, then try the series of cancels. No harm will be done to your engine in the meantime.

If that doesn’t get you anywhere after a month or so, perhaps the sensor does need changing. It is only a sensor and with no feedback that may cause any harm. The worst that can happen is that it makes no difference and you’ve wasted time and whatever it cost you. I will add however that the software should be updated after replacing NOx sensors - those limits I talked about earlier may get reset.

 

[JuannyH]

I can only comment that I’ve had the same issue - the fault code reappearing after different time periods. Those varying time periods roughly align with different usage: just short trips and it’s back on within a week; a couple of long trips and it’s over a month to reappear.

My conclusion is that it’s not faulty sensors, but instead tight limits on the accepted range in the software. The short trips clogging up the sensitive sensors quicker, then cleared during a long trip.

I‘ve persisted with cancelling the warning with my reader, and after a few repeats the EML stays off for a year or so. Then it’s repeat. It only takes a couple of minutes to do the cancelling, so it’s no big deal. It’s a lot easier and vastly cheaper than replacing sensors.

My recommendation, for what it’s worth, is to give the car an “Italian tune up” (a good blast) to clear everything, then try the series of cancels. No harm will be done to your engine in the meantime.

If that doesn’t get you anywhere after a month or so, perhaps the sensor does need changing. It is only a sensor and with no feedback that may cause any harm. The worst that can happen is that it makes no difference and you’ve wasted time and whatever it cost you. I will add however that the software should be updated after replacing NOx sensors - those limits I talked about earlier may get reset.

Thanks for that! I do short trips and next year am due a much longer 5 hour trip so maybe that will work! I’ll see if I can do the trip without holding my breath!

 

[toshy816]

I've been trying to read as much information as I can find about NOX sensor problems and the best way to approach the problem. First let me say that I am not a vehicle tech and stopped crawling under my cars years ago, and for the last 30 years or so have had what `I consider to be good quality cars, Mercedes, BMW, Saab, and VW. My current car is a 16 plate c250d and for the first time in 30 years had a warning light that said there was a problem with the NOX sensor. I took it to a Mercedes trained tech in Mansfield who runs his own business who told me that my car was under recall with Mercedes and so I took it there. They reset the warning light but said the cost of a new sensor was not covered in the recall and new replacement job was over £700.

I didn't go ahead and now the sensor comes and goes, sometimes a few weeks on and a few weeks off, but the performance of the car does not seem to be affected in any way.

I've recently given thought to taking it to a remap/adblue/NOX resetting centre to have it disabled but have just read that it is illegal to run your car on the road if you do this. Can anyone confirm this?

 

[TC350]

I've recently given thought to taking it to a remap/adblue/NOX resetting centre to have it disabled but have just read that it is illegal to run your car on the road if you do this. Can anyone confirm this?

It may or may not be illegal, but how would anyone know?

 

[rf065]

I've recently given thought to taking it to a remap/adblue/NOX resetting centre to have it disabled but have just read that it is illegal to run your car on the road if you do this. Can anyone confirm this?

Yes it is illegal, but, it will pass every MOT, unlikely that anyone will ever know you've done it, and you will save yourself £1000's in future repairs.
I had it it done 3 years ago and have never regretted it.