Recurring NOX sensor issue on 16 model C200 Coupe (petrol)

MKCambs

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This is my first post to these forums, so apologies in advance if this is not the right place to post and if so please feel free to move it to a more suitable forum.

My 16 plate C200 Coupe (petrol) has a recurring NOX sensor problem. The amber engine warning light comes on and during the service the diagnosis points to a NOX sensor issue.

The car is on very low mileage (only about 3900 miles in 2 years).

I bought the car in March 16 brand new from Robinsons Mercedes in Cambridge and it has only been serviced by them.

The problem occurred for the first time in Nov 16, then in Jan, Feb, April, May 17 and now again in Mar 18.

So far Robinsons Mercedes have been unable to provide any clear explanation about the root cause of the problem or how to completely resolve it. In some cases they've even said that they could not find out what the actual issue is and just reset the warning light. The last time they looked at it, in May 17, they said they replaced the NOX sensor, took the electronics apart and reassembled them and they were confident the issue has been fixed - well, only for 10 months!

I am worried about what will happen after the car is out of warranty (next year, in Mar 19), if the issue keeps recurring after then.

My questions:
  • Has anyone else had similar problems with NOX sensors on their Mercedes?
  • Is it a known problem with Mercedes, is it only seen on specific models?
  • Is there a known solution for this problem?
  • Could it be related to the usage profile, i.e. low mileage? (that was mentioned as a possible cause by Mercedes service)
  • Could the underlying cause be a more serious fault with the car?
  • For recurring problems such as this, what happens when the warranty runs out?
Any information and advice would be greatly appreciated.
Thanks!
 

John Laidlaw

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Not had this issue personally and not heard much on petrol cars either. (On diesels contamination might cause it I guess ). Interesting to hear what others say on this, I wonder on the low mileage whether temperature shock could be knocking the sensor out or something CAT related?
Oh and on warranty, any reported issue which is on going should still have cover but I’d flag this to MB
 

LostKiwi

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Hi and welcome. I do seem to recall this coming up before and it being pretty common when you dig a bit further.
The good news for you is that MB warranty parts for 2 years so even if you're out of warranty you still have warranty on this part. And as it's a long standing issue you should be able to successfully argue it's a warranty issue as it occurred before the warranty expired and was unresolved.
 
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MKCambs

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Thank you for the good advice. I have forwarded my concerns to Robinsons Cambridge. It's strange that this is such a difficult problem to fix.
 

AJD

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Hi MKCambs, welcome to the forum. Instant sound advice you have there :)
 

DrDTK

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Hi MKCambs, I had a NOx sensor replaced at 11300miles under warranty, 18months later and another 11000miles, MIL light on again so suspect another NOx sensor failure, waiting for fault codes to indicate problem.

I have found from previous research that NOx sensors can be damaged by poor fuel quality, particularly due to sulphur, do you use premium fuels like Shell, BP or supermarket? and what grade of fuel?
 
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MKCambs

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I have used supermarket fuel a few times after buying the car (that was 2 years ago). Then after the first NOX sensor issue (suspecting it could be related to fuel), I switched to Shell V-power. Since then, the issue has occurred 5 more times. So I am not sure if has anything to do with it. But maybe the few times of using supermarket fuel initially has damaged the system, who knows?

BTW, an update since my last post:

The car has been serviced by MB after the engine warning light has come on. They have said that the diagnosis showed a "stored" fault which was not present and had occurred once. The electrical connections were checked and the software was updated. The NOX sensor was not faulty, so it was not replaced.

They think that the low mileage (only 4000+ in two years) and short journeys could be contributing to the problem, so they suggested I drive the car over longer distances e.g. on weekends.

Any ideas about their claim, i.e. if the low usage of the car could be the cause of the problem or not?
 

grahamcol

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I'm not convinced low mileage has anything to do with the problem. Both of my cars have covered little mileage in the last two or three years and neither one has displayed any problems with the engine or emissions equipment.
Good luck.
 

John Cross

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I also have a recurring Nox sensor fault on my C200T 2014 model now covered 20,000 miles Mercedes serviced BP Ultimate always used !! Last one fitted under warranty 9 months ago. Booked in next week for B service and cure warning light. Believe me when I say if this is not rectified under a goodwill gesture Mr Savage at Mercedes MK will be receiving yet another letter from me regarding this most unreliable car! Sorry to moan in my first post. I do however enjoy the car despite the many faults. John Cross
 

Taffy7hfa

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I also have a recurring Nox sensor fault on my C200T 2014 model now covered 20,000 miles Mercedes serviced BP Ultimate always used !! Last one fitted under warranty 9 months ago. Booked in next week for B service and cure warning light. Believe me when I say if this is not rectified under a goodwill gesture Mr Savage at Mercedes MK will be receiving yet another letter from me regarding this most unreliable car! Sorry to moan in my first post. I do however enjoy the car despite the many faults. John Cross

Calling a 4 year old car unreliable because a warning light has come on seems a little harsh ;)
warning lights will occasionally light up, they rarely mean the engine is about to implode, however
its interesting how often it is assumed they have a "faulty sensor" my experience for what its worth is that the sensors are often working perfectly well, its just much easier to say "aahh yes its probably just a faulty sensor" than to try and diagnose the actual problem.
 

John Laidlaw

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I also have a recurring Nox sensor fault on my C200T 2014 model now covered 20,000 miles Mercedes serviced BP Ultimate always used !! Last one fitted under warranty 9 months ago. Booked in next week for B service and cure warning light. Believe me when I say if this is not rectified under a goodwill gesture Mr Savage at Mercedes MK will be receiving yet another letter from me regarding this most unreliable car! Sorry to moan in my first post. I do however enjoy the car despite the many faults. John Cross
Welcome John
 

John Cross

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Believe me this was not the only problem. Boot close module. Main body control Ecu which then required new nav disc. Arguing the cost of this was fun. Along with various door illumination faults. All expensive items. I should at this point explain my previous 4 cars were Honda Accords. Not one warranty fault on any model. My other car is Mazda mx5. Again faultless!! But I still like the Mercedes. Must be mad. I’ll let you know if the nox sensor is replaced foc somehow I doubt it. The road holding with the air suspension is good. The roof opening is nearly as good as my mx5 the mpg is good for a very fast accelerating car. Seating is comfortable. I feel happy driving the car despite Mercedes insistence on a silly hand control auto gearbox change lever? And hidden cruise control lever which should be on the steering wheel. I must be mad. Thanks to all. John
 

Mark-t

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The garage where my C200 2014 petrol is serviced is saying that my driving style, Miss Daisy, car in comfort setting, auto, never driven hard is not helping the nox issue. They suggest on occasion put into sport mode use the steering wheel paddles when engine hot and get to 4000 revs before changing gear. I’ve never been a boy racer type. Garage offered to take on run for me. They are saying car on occasion needs to be driven hard. Not sure if this explains people repeated faults. Mark.
 

Mark-t

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The garage where my C200 2014 petrol is serviced is saying that my driving style, Miss Daisy, car in comfort setting, auto, never driven hard is not helping the nox issue. They suggest on occasion put into sport mode use the steering wheel paddles when engine hot and get to 4000 revs before changing gear. I’ve never been a boy racer type. Garage offered to take on run for me. They are saying car on occasion needs to be driven hard. Not sure if this explains people repeated faults. Mark.
8/9/2018 Update. Following my local car dealer clearing the fault. I tried to drive as directed. With engine warm after 16 miles of Miss Daisy driving put into sport mode and used the paddles and after about a mile the engine warning light came on.
I took this to my regular service garage, not Mercedes. He rang Mercedes and they said I must take to a Mercedes dealership and at 4 years old with 18,000 miles on clock, all being well Mercedes may well do under warranty. It goes in next week. They say software update may sort. I wonder if this is a known issue with this model.
I will let you know how I get on.
 

Anicho

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I had the same problem of engine maintenance light on dashboard. Nox sensor error on c200 2014 petrol . Replaced once within one year. Same error now. Croydon Mercedes charging me around £600 for replacing it as it is now out of warranty period. I don't do many miles. Seems to be a systematic fault on these models.
 

Big Burd

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I'm a newby.
2016 C200 coupe, bought 2019 with 8000miles, currently 17,000.
Engine management light came on, no apparent problems, 300 miles later my local garage did a diagnostic, NOx sensor
Have booked into dealer for diagnostic check (3 weeks and 900 miles after 1st diagnosis).
Car is running perfectly, mpg as normal, no smoke.
Seems from the above posts this happens.
Can people tell me what I might be told, what to expect? I dont want to be spoofed!
 

Botus

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On many Diesel Merc's this age they need some later software.... then lots of new parts once the software update tells you the modified parts to fit.... then some new software to go with the new hardware (NOT JOKING)

on a Petrol it might be less designed in fun - but most indepenant garages can't do the software updates regardless - I'd start with someone with online STAR kit so they can do programming updates if it (likely) needs it...

where u hiding STAR at reading berks are very good with sensible prices and all the kit
 

Big Burd

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Thanks for that! I just feel very much at the mercy of the dealer, getting blinded with science!
First step is "initial" diagnosis, which may lead to "in depth" diagnosis. I'll post the initial response.
In Somerset.
Meanwhile, the car (petrol) is performing fine
 

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