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!