R231 Mercedes SL350 P2201 Nox Sensor Fault

pavanpaw

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Hello all - firstly thanks so much for your help in advance!

My engine management light on my 2014 SL350 keeps on coming on.

I've read the fault using a cheap meter, which is coming back as P2201 - NOx Sensor Circuit Range / Performance Bank 1. An independent Merc garage has also said that it's one or two of the NOx sensors at fault.

Mercedes direct are being really awkward and are saying that I need to take the car in for more diagnostics - at a cost of an additional £320. They also said that the cost would be £1200+ to replace both sensors, if they go ahead with the repair after running diagnostics.

Some questions:
  1. Does anybody have experience in fixing this fault?
  2. Would cleaning the sensors potentially work, or do I need a new sensor?
  3. Can I replace just one sensor, or would I need to do both?
  4. Where are the sensors located? Mercedes are telling me that the seats will have to come out.
  5. Has anybody had luck in having Mercedes sort this out, after the warranty period?

Thank you so much in advance!
 

mersum1es

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Did you ask if it would go in goodwill? They has been under GW...
 

alexanderfoti

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1. Yes, this is quote a common fault and the sensors do go
2. Not usually
3. Only the sensor that is actually at fault, but the other may fail shortly afterwards (or never, but they do tend to faul at the same time.)
4. They are connected into the exhaust, but to access, both front seats and the rear passenger side trim need to come out.
5. Some users have had luck pushing for "goodwill" from MB.
 
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pavanpaw

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1. Yes, this is quote a common fault and the sensors do go
2. Not usually
3. Only the sensor that is actually at fault, but the other may fail shortly afterwards (or never, but they do tend to faul at the same time.)
4. They are connected into the exhaust, but to access, both front seats and the rear passenger side trim need to come out.
5. Some users have had luck pushing for "goodwill" from MB.

Thank you so much both.

@alexanderfoti - do you happen to know if people have had luck in simply updating the software instead of replacing the sensors?

Also, would you recommend changing them in a pair even if only one has a fault?

Many thanks in advance
 

mersum1es

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Softaware update is needed if newer type sensor module is fitted. Won't repair sensor fault.
 

goodoldfred

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Softaware update is needed if newer type sensor module is fitted. Won't repair sensor fault.
Hi !

By any chance do you have any further information on the software update ? I have a similar car and the dealer (independent) said there was a compatiblity issue with the most recent Nox sensors and he had to install an ECU software update before he could replace the sensor. I'm curious to know more because since I got the car back it's been a lot more fun to drive than it has been in all the years I've had it. ECO mode is now closer to what SPORTS mode was before. I asked the dealer for more information but he didn't get back to me.
 

mersum1es

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Hi !

By any chance do you have any further information on the software update ? I have a similar car and the dealer (independent) said there was a compatiblity issue with the most recent Nox sensors and he had to install an ECU software update before he could replace the sensor. I'm curious to know more because since I got the car back it's been a lot more fun to drive than it has been in all the years I've had it. ECO mode is now closer to what SPORTS mode was before. I asked the dealer for more information but he didn't get back to me.

I have no better information but I am pretty sure it does not improve you engine performance, more like opposite (old software has been too optimistic, not giving promised emission leveles. Heard few cases where adblue consumption increased heavily after update)
 

goodoldfred

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I have no better information but I am pretty sure it does not improve you engine performance, more like opposite (old software has been too optimistic, not giving promised emission leveles. Heard few cases where adblue consumption increased heavily after update)
Hi ! This is a petrol engine but either way it's running differently. Much better pickup from low revs. More sporty for sure. Have to see if there's any difference in petrol consumption in the course of time.
 

mersum1es

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Hi ! This is a petrol engine but either way it's running differently. Much better pickup from low revs. More sporty for sure. Have to see if there's any difference in petrol consumption in the course of time.
AH! Ok I have no experience how gasoline engine nox sensor is used in control system.
 


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