What to do? NOx sensor code AGAIN

[Deleted member 65149]

My 2012 C350 PETROL has only covered 36k miles but the NOx sensors have been replaced twice. The first time was just before the three-year warranty ran out and the second time was in September 2019. The car has covered less than 5,000 miles since the second change of sensors.

Back in May the EML came on so I plugged in my cheap OBDII reader to be told "P2214 NOx Sensor Circuit Range/Performance Bank 2". I did a reset to clear the EML and all was fine - for a short while. I've since done this several times at intervals roughly depending on mileage covered or days elapsed, but often just leaving the EML on and ignoring it.

A couple of weeks ago I put the car into my local MB dealer for its A Service and MoT (I've always had the services done there from new). Just before taking it in I reset the EML after reading the P2214 code again. No problems were reported and all the MoT checks passed. The Lambda reading was 1.002, nicely centred within the limits of 0.970 to 1.030.

Now here's my dilemma. The indications are that NOx sensors are failing again. Or are they?

So do I take it back to the MB dealership and again pay them £110 (or whatever it is now) for them to do a quick code check with probably the same result and, assuming they say the NOx sensors need replacing, get them to do it under the 2-year parts warranty? But does the parts warranty cover labour? How certain can I be that there's not some other issue that's causing the sensors to show up as failing and that the MB mechanic isn't looking for other possibilities but instead is only doing what the plugged in computer is telling him to do?

Alternatively, do I take the car to an indy (the only one I know in or near Peterborough has a good reputation but doesn't specialise in Mercedes, they also work on BMWs, Porsches and the like) and get them to check things over in the hope that they're more likely to look deeper into the issue? If they conclude that the NOx sensors have to be replaced, can I assume that the parts will still be covered by the existing warranty on them?

What should I do? Any advice please?

 

[dmb007]

I posted this on the forum about May last year.


I have seen many posts regarding EML problems and I would like to add my experience re this problem.

I have had problems since last Jan (2019) with the EML light being orange on my E400.

The selling MB dealer initially cleared the fault and that worked for about 3 months before the EML came back on.

It took the dealer a further 3 visits (over a period of 9 months) to individually change 2 NOx sensors and a temperature sensor.

I was told that all sensors had now been changed as there were only 3 to change. So that should be problem solved.

BUT I asked (as my warranty period was coming to an end) if these new sensors would be warranted for a further 12 months.

The answer was no.

I visited another MB dealership.

Long story short there are 5 sensors not 3 on the E400.

My understanding of this is (and someone please correct me if I am wrong) that there is a sensor at beginning of the exhaust system and at end
of the exhaust and a temperature sensor to activate system when up to temperature.

On the E400 it as a twin exhaust requiring 2 NOx sensors at the front and 2 at the rear plus temperature sensor.

So the new dealer replaced the sensors provide a 2020 C300 courtesy car and MB paid for the replaced sensors.

It remains to be seen whether the fix is permanent(long lasting) but I have more confidence with the new dealership to deal professionally and timely with any future problems.

Here's hoping I will not see that light for some time.


So touch wood things are have been ok since. I would add that a software update was required that original dealer did not do. Not sure on the C350 the engine size and exhaust configuration.

But I would mention that the second dealer did not know the number of sensors on first attempt to fix.

Personally I would always go back to the Main dealer as I don't think an independent would do FOC.

My first Main dealer, part of a national group, as since closed down.

Not sure if this helps but best of luck sorting this out.

Regards
David

 

[Deleted member 65149]

I posted this on the forum about May last year.


I have seen many posts regarding EML problems and I would like to add my experience re this problem.

I have had problems since last Jan (2019) with the EML light being orange on my E400.

The selling MB dealer initially cleared the fault and that worked for about 3 months before the EML came back on.

It took the dealer a further 3 visits (over a period of 9 months) to individually change 2 NOx sensors and a temperature sensor.

I was told that all sensors had now been changed as there were only 3 to change. So that should be problem solved.

BUT I asked (as my warranty period was coming to an end) if these new sensors would be warranted for a further 12 months.

The answer was no.

I visited another MB dealership.

Long story short there are 5 sensors not 3 on the E400.

My understanding of this is (and someone please correct me if I am wrong) that there is a sensor at beginning of the exhaust system and at end
of the exhaust and a temperature sensor to activate system when up to temperature.

On the E400 it as a twin exhaust requiring 2 NOx sensors at the front and 2 at the rear plus temperature sensor.

So the new dealer replaced the sensors provide a 2020 C300 courtesy car and MB paid for the replaced sensors.

It remains to be seen whether the fix is permanent(long lasting) but I have more confidence with the new dealership to deal professionally and timely with any future problems.

Here's hoping I will not see that light for some time.


So touch wood things are have been ok since. I would add that a software update was required that original dealer did not do. Not sure on the C350 the engine size and exhaust configuration.

But I would mention that the second dealer did not know the number of sensors on first attempt to fix.

Personally I would always go back to the Main dealer as I don't think an independent would do FOC.

My first Main dealer, part of a national group, as since closed down.

Not sure if this helps but best of luck sorting this out.

Regards
David

Thanks David. Our engines are the same size, but mine is naturally aspirated, and I think the exhaust layouts are similar. Your different experiences with different main dealers confirms my doubts about how well they actually know their cars. Mine, that I use for convenience with it being only a 30 minute walk, have always been very pleasant and as helpful as they can be but they've never fully convinced me that they are fully on top of what they're doing. In the dim and distant past I had trouble with a main BMW dealer who took a lot of convincing that they'd done a job wrong. But I've also experienced independents showing a lack of knowledge in some areas.

I hope yours stays clear. As I said, my NOx sensors were replaced in September 2019 but already appear to have been playing up since this May.

 

[Benz17]

So unfortunately it’s not just diesels that are having problems with the Nox.

 

[DSM10000]

I very much doubt that an MB garage will replace the sensors under the 2 year parts warranty on the diagnostics of a rival independent garage.

 

[Deleted member 65149]

I very much doubt that an MB garage will replace the sensors under the 2 year parts warranty on the diagnostics of a rival independent garage.

I wouldn't expect them to. I was wondering whether the parts warranty was for the parts alone or if it also included labour to replace them. If the latter then I'd be more likely to go to the main dealer.

 

[pmcgsmurf]

If they were fitted by the main dealer and are now faulty if they diagnose them as faulty again then they will fit for free and should also refund any charge for diagnostic.

We had a faulty pump removed from a 651 and had a bit of hassle trying to get this changed under warranty. Wanted the car took into them for them to check.

Took the pump to the parts department and they replaced it in the end.