Knock Sensor needs replacing exhaust - quoted £1200!!!! :(

[Portugeezer]

Well, mine was done our of warranty, I think you have a good chance, low mileage, always services at MB, and it's a known issue. You should state that when you take into

 

[grober]

The "oxygen sensor" may have been your lambda sensor which is used to regulate the air/fuel ratio- might explain the change in your fuel consumption? NOx sensors are not unrelated because they function a bit like a double lambda sensor. The thing that kills them evidently is water vapour meaning the exhaust has to up to a certain temperature monitored by yet another pre-sensor [ exhaust gas temperature] before the NOx sensors are switched on??
W205 NOx Sensors Fail

 

[Uky]

E350 CGI (Petrol) M272 (Well above all "problem" serial numbers...)

Even I today...
..Experienced the EML coming on. Being close to a friend that works at an MB service center
the error codes was for the NOx sensors, both sides. Upper limit was 4.5 (something).
One of the sensor readings was 4.6, the other 4.8. We also saw error codes
for high exhaust temperatures. The engine however - ran as smooth as ever.

We updated the engine controller software (Xentry displayed a notification
of a sugested update) and also resetted all error codes. Way back I ended up
in a traffic jam at the highway (+30C) for about half an hour but the EML did not came back.

Question: Is it possible to replace the sensors
on my own and will the EML go off after replacement or do I have to
clear the EML with a diagnostic tool? Does new sensors have to be adjusted
or configured for my vehicle?

 

[Uky]

Answer: According to my friend - No - The sensors comes with their own "controllers" and has
to be initiated and SCN-coded to the vehicle...

 

[clk208]

Answer: According to my friend - No - The sensors comes with their own "controllers" and has
to be initiated and SCN-coded to the vehicle...

Interesting. Let us know how you get on. Are the sensors pricey on this era of engine? Haven’t read about these going on an M272 before.

 

[Uky]

When - (I am a 100% cynic) - the EML comes on again, the sensors will have to be replaced
of course. I have no idea of if they are pricey. I know that there are a number of part numbers
for them as Mercedes seemingly have had problems with them. The service record states that there
was a problem with high exhaust temperatures in the past related to an EGR-valve
but I have no copies of invoices so I do not know if something has been replaced.
My primary concern was if it was the timing chain idler as this is a € 5000 job...

 

[Portugeezer]

Mine is going in again on Tuesday, strange thing is the EML sometimes goes off, then twenty mins or so later comes on.

 

[Portugeezer]

I've read in other forums the engine can be remapped to ignore the sensors and adblue system - has anyone done this - is it a good idea?

 

[Uky]

(A reminder that this thread deals with both diesel and petrol engines and mine is an M272 350CGI petrol with NOx sensors.)

Since friday I have travelled 350 km with the vehicle while the temperatures has been +30 C and well above.
Highway speeds, Been stuck in traffic jams, Towed a wagon filled with scrap (400+ kg) to a recycling station. No EML.

I wish I knew what MB has changed in the software upgrade that was applied.
In some cases, based on experiences with other vehicles, it can be a wider (relaxed) tolerance
of readings, an implementation of a certain number of "over-the-threshold-readings" that has to occurr before the EML
comes on, and/or a combination of resetting such a counter when turning off the engine.

 

[Portugeezer]

Car in today at MB in Poole, last night went on a longish run on the motorway, high revs in sport mode, engine light did not come on.
Took to MB in Poole today 1 mile from the garage engine light comes one!
Maybe I have to drive at high revs in sport mode all the time !
Anyway will post on here when I get the update from MB

 

[Petrol Pete]

The "oxygen sensor" may have been your lambda sensor which is used to regulate the air/fuel ratio- might explain the change in your fuel consumption? NOx sensors are not unrelated because they function a bit like a double lambda sensor. The thing that kills them evidently is water vapour meaning the exhaust has to up to a certain temperature monitored by yet another pre-sensor [ exhaust gas temperature] before the NOx sensors are switched on??
W205 NOx Sensors Fail

I just love the simplicity of a diesel engine .

 

[Portugeezer]

Well this is a good story, MB told me last time that both nox sensors had failed and needed replacing and they would replace both. Well it appears they only replaced one last week and replaced the other today! So appears fixed. Sadly as MB footed the bill they said there is no warranty on the parts !
Makes me think they didn’t replace them and just reset the error....

 

[grober]

This is a contentious issue and depends on the exact terms of the warranty. If a part is replaced for free under the warranty it doesn't have the usual 1-2 year part's warranty of a purchased unit [ from date of fitting]--- however its my understanding that aforsaid part fitted as part of a warranty repair assumes the identity of the original defective part meaning it benefits from the remaining manufacturers warranty. So if your EGR packed up after 2 years of a 3 year warranty and was replaced it retains 1 year of the manufacturer's factory warranty cover if it faults again. ----- subject as always to routine MB servicing and fitting conditions of course!

 

[Deleted member 65149]

(A reminder that this thread deals with both diesel and petrol engines and mine is an M272 350CGI petrol with NOx sensors.)

Mine is an M276 350CGI with NOx sensors. The bloody things don’t appear to discriminate between engines.

The software tweak to relax the tolerances sounds interesting. Reminds me of very many years ago when I was working with various top manufacturers to develop copper telecommunications cables for greater transmission bandwidths. A group within BT headquarters had provided a target specification that all the manufacturers had been able to meet except for one thing. For many months they all tried all sorts of adjustments to designs, materials and construction methods but to no avail. At best they were still falling short of the target by around ten percent. Eventually I went back to the specification’s author in BT and explained the position, declaring that aspect of the specification impossible to achieve. The response, “Don’t worry, I just plucked the figure out of the air. You can drop it by 20%”. Grrrrrrrrrrr

 

[MSG2004]

Interesting thread.
I've private messaged the Matty the thread starter here.
So many parts to go wrong on newer cars and it appears some problems are quite common because of parts
not up to the job and the poor MB buyer gets hit.

 

[Deleted member 65149]

I’m pleased to report that Mercedes have agreed to knock £1,000 off the bill for replacing my NOx sensors, even though my car is 7 years old. Their customer service seems better than some of their parts.

 

[MSG2004]

Thanks Matty for the response to my PM today and I have sent you you another thanking you.

Summary - car GLE 250d just under 3 yrs 5 months old - serviced by MB 2 months before and had only covered 200 miles or so BlueAd warning messages and engine management light - had MB rescue come out - car to MB and told them re this common problem, they said they'd look into it and within a few days cars fixed at no cost other than the worry, time and effort by me and they gave us a free loan car as well, E class was around so got that - I think it's whom you deal with and this breakdowns customer service lady was very nice, caring, informative, listend to my concenrs and why i felt it was the Nox sensor and told her I blog her as well - but bottom line is she was on the ball we too were noce and polite and they agreed that my car was well looked after and Nox should have not broken down. I take my hat off to this young lady.

 

[Deleted member 65149]

Just an update on the NOx sensors on my seven year old C350. They were replaced today and £1000 knocked off the bill as promised. The car somehow feels even smoother - but probably my elation at not having to pay £1200 has left me light headed.

Thanks to Matty for his help on this one, as well as others who have reported success. MB got it wrong with these sensors but at least they're doing the right thing now. That's why we love the brand.

 

[MSG2004]

Apologies if I've not made myself clear.
MB replaced one of the Nox sensors FOC.
IMO, it's whom you deal with.
The young lady we dealt with, listened to my
one min summary of events. And one polite
facts about the FSH by MB and car had
covered less than 15k miles and just been serviced, one driver.
The young lady said leave it with me, sir. We did
and thanks to her, saved us close to a k I think.
Btw, hats off to the MB customerCare Service guy
that came to see the car.
MB dealer agreed car was like new and could tell as no marks inside or
on tyres/wheels other than it being keyed.
I'm a shy kind of guy and have worked in the front line
of social services and know what it feels like being ranted and raved at by misfits.
So, remain polite, calm, factual and state your case in a short, concise summary.

Thank you all that helped here.

 

[SomT]

Hi! I realise this thread is quite old, but I just came up against this problem. I have an electric diesel hybrid (C-class saloon), year 2014, which I just got 2 months back (purchased second hand), and now I have the yellow light on the dashboard as well. When I took it in to get a diagnostic done, I was told that the Nox sensors and an air filter are gone and need replacing. (I was given the part numbers). I was quoted £1200+ for this job, which is kind of crazy.

I found it very interesting to hear that you called Mercedes and that they covered your costs.

I do have a 6 month warranty, but they will only cover upto £500 of each claim, so it would still cost £700+ for this job.

Of course, I probably wouldn't get that benefit, but I was wondering if I could buy the parts online, which would be a lot cheaper (if I quote the part numbers and ensure they are the correct ones) and then get it done from any other service centre.

Any recommendations would be welcome.

Also, in this current condition, how long can I drive the car? I'm only counting on a few days and miles at most - basic errands, shopping, etc.

Thank you so much!

Update Nox Sensors:

Got a call from my local Mercedes Dealership regarding my call to MB Head office.

GREAT NEWS GUYS / GIRLS!! Mercedes are covering 100% of the cost as a good will gesture!

Mercedes HO offered 65% contribution and it was my local dealer that contributed the rest. Reason for that was that I bought my car new from that dealership and have used their service department for 5 years.

I was jumping for joy. My car also needed a gear box service which I was gonna wait for but while it was in i book that in to.

Gear box service for my 63 reg e350 came to £230!! I thought that was very cheap, I was told a discount was put on their including my diagnostics charge refund. Again I was very pleased with this as i though it was around the £500 mark.

My love for Mercedes has been restored. Now I just hope this new sensors last.

Want to also thank the forum and everyone who has replied to my post. Without you guys I wouldn’t of had this problem resolved and would of been £1200 short. Will post a last update when the jobs have been completed.

Thank you all.



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