NOx - Understanding How Many Of Us

[OldskoolRS]

We've got an engine management light on the dash on our 2016 W205 C200 petrol and my iCarsoft reader confirmed it is the post cat 02 sensor. My brother in law had similar not long after he bought his C200 last year, but was covered as it happened not long after purchase (non MB dealer). I'm assuming this is the same, or at least similar sensor to that discussed in this thread?

Ours doesn't have any service history since we bought it 2 years ago as I made the decision to DIY it as we plan to keep it many years, by which point I'd laugh at any buyer expecting FSH. Therefore I'm minded to just try a non MB part and see how it goes. I've cleared the light, but it comes back after a couple of journeys and the MOT is due next month, plus we plan a longer journey to visit my family in June, so would be best to get it sorted soon.

I plan to confirm I've got the right sensor by clearing the light, then disconnecting the one I suspect and see if I get the same/similar error message on the iCarsoft.

I know some will throw their hands up in horror at not using MB parts, but has anyone fitted an alternative parts and have you any feedback? I suspect my BiL's car has a non MB part fitted, but he isn't local and not very car savvy.

 

[MBCF]

Anyone know what the code is for the emissions recall?

I just had my W204 C class 2011 back on Friday, I told them not to do the emissions update - the printout they gave me shows "ESS LAB N/Q D&G recall" under work completed.

Took my car on the motorway today, by the time it hit 60 it sounded like a plane was taking off and got louder as I got to 80, could not test beyond that due to traffic.

Noise was coming from the left side under the hood, when I sped up to check the engine made a familiar noise revving up but was still being drowned out by the other sound that I have not heard before on this or 2 E classes.

Have not had a chance to read all 10 pages of this thread - anyone else had this issue?

Will need to book it in again with MB.

 

[MBCF]

Had an update from MB:

"ESS LAB N/Q D&G recall – Is our reference for Labour not quoted, D&G means drop and go appointment., RECALL was booked but NOT DONE as per your request no ECU updates to be done."

ESS shows as electronic service sheet according to a quick google search.

The car went in for a subframe replacement, I specifically told them not to do the emissions recall. They claim to have not done it, the question is why is recall listed?

Took the car for another drive for a second opinion, the noise can be heard from approx. 45mph upwards, continues when I lift off the accelerator pedal and the second opinion was it may be the turbo.

Does not seem to affect the car in any way, speeds up as normal to 80 but the sound was definitely not there in the previous 3 years I have had the car.

Also had the drop link on the front left and shock on the rear left changed, but the noise does not sound like it is to do with that.

Is there a straightforward way to check if the emissions update was completed and if so when? Take it to another dealer?

 

[rf065]

Had an update from MB:

"ESS LAB N/Q D&G recall – Is our reference for Labour not quoted, D&G means drop and go appointment., RECALL was booked but NOT DONE as per your request no ECU updates to be done."

ESS shows as electronic service sheet according to a quick google search.

The car went in for a subframe replacement, I specifically told them not to do the emissions recall. They claim to have not done it, the question is why is recall listed?

Took the car for another drive for a second opinion, the noise can be heard from approx. 45mph upwards, continues when I lift off the accelerator pedal and the second opinion was it may be the turbo.

Does not seem to affect the car in any way, speeds up as normal to 80 but the sound was definitely not there in the previous 3 years I have had the car.

Also had the drop link on the front left and shock on the rear left changed, but the noise does not sound like it is to do with that.

Is there a straightforward way to check if the emissions update was completed and if so when? Take it to another dealer?

Emissions update doesn't change the sound of the engine or anything else.

 

[OldskoolRS]

The car went in for a subframe replacement,

Is it possible that they disturbed the exhaust doing this replacement? Maybe it is touching somewhere and causing a resonance?

 

[SpikyMikey]

Is it possible that they disturbed the exhaust doing this replacement? Maybe it is touching somewhere and causing a resonance?

Or an intake hose ?

 

[MBCF]

Is it possible that they disturbed the exhaust doing this replacement? Maybe it is touching somewhere and causing a resonance?

The sound is coming from the front left, only kicks in above 45mph. From what I saw the exhaust comes from the right and goes underneath the centre of the car?

 

[MBCF]

Or an intake hose ?

Is that located in the front left, the second opinion was a loose hose? Planning on taking it back to where I had my front left drop link done and asking them to check tomorrow morning.

 

[MBCF]

Emissions update doesn't change the sound of the engine or anything else.

They also told me back in 2020 that it was not the cause of my EML coming on my W212. This is almost certainly not coming from the engine.

 

[SpikyMikey]

Is that located in the front left, the second opinion was a loose hose? Planning on taking it back to where I had my front left drop link done and asking them to check tomorrow morning.

To be honest, I don't know, but if your noise is a 'woosh' on acceleration, it can often be down to a split intake/intercooler/egr pipe.
Given your car has been in for work recently, maybe something got damaged/dislodged/not put back together properly. It happens......

 

[MBCF]

To be honest, I don't know, but if your noise is a 'woosh' on acceleration, it can often be down to a split intake/intercooler/egr pipe.
Given your car has been in for work recently, maybe something got damaged/dislodged/not put back together properly. It happens......

Not a woosh on acceleration, a sustained nose above 45mph, accelerating or not. Suspect it is something to do with air intake.

 

[edgersoldchap]

Edgersoldchap

Interesting post, but I suspect there's a bit more detail required to fully understand what you have had done and how that relates to other people's problems with regards to the NOx sensors............................................................

I trust some of that is of interest and makes you feel a bit better than the tales of doom.

Best Regards.

The only detail that I can add to my previous post is what is shown on the MB invoice - 'Downstream NOX (1.5). MA905 81 11 083269/NOX Sensor.'

I have no idea what gen SCR my car has fitted - you could well be right in your assumptions. For just 'an owner', you have acquired an impressive depth of knowledge on the subject., whilst for me, I read all sorts of things about issues that might affect my car but at the first sight of trouble take it to an expert to identify and sort it. I left behind me long ago the desire (and knowledge/ability) to do anything about it myself - probably as a result of blowing up the engine of a Hillman Imp 50 years ago when I dropped a washer from the Stromberg carburettor I was attempting to clean, unknowingly down the inlet manifold.

As far as software updates are concerned, I have no idea what has been done over the car's lifetime before my ownership. All I know is that there are no outstanding updates.

Thanks for the tip about taking a run up the motorway to get the SCR system to reset correctly - any idea how far I need to go!

Anyway, with all these issues around NOx sensors, AdBlue etc (not to mention DPF's, clogged injectors etc), I have decided that I will trade in my E220d for a petrol engined estate, probably a BMW as an E200 has no appeal and I don't need an E43 or E63 - I have a Jaguar XKR with 5.0 litre supercharged V8 for hooning about. Since retiring, I no longer do the mileage to justify having a diesel, and hybrids or full EVs do not interest me. I don't buy into the fiction that by having one, I will contribute to saving the planet - but that's a discussion for another day, certainly not here!

Thanks for taking the trouble to respond so comprehensively with some thought provoking comments - much appreciated.

 

[EdPhil]

Edgersoldchap:

I am glad you appreciated the detail; here’s a little bit more. Don’t forget that it’s just what I have come to understand during personal investigations, and I certainly don’t claim to be an ‘expert’. I think my basic problem with ‘experts’ is that I have worked with ‘experts’ in many technical fields during my life and far too many people are given that accolade just because they know a little bit more than the average layman. I can think of lots of examples where ‘experts’ mislead most people towards problems that a bit of critical thought might avoid.

You may not be that interested in this, but it’s probably interesting to other DIY owners of SCR Mercedes who don’t just want to rely on others. For the ‘confused’ people above: a vehicle’s lambda sensor is NOT the same thing as a Smart NOx sensor. I have included a copy of details of NOx sensor numbers and notes from a working file of mine for information at the end - why not share? It may be necessary to read previous posts to understand what this is about, and I doubt that I will spend much time in future adding further detail as my Gen 2 CLS seems to be fine now (code 03o fix). The original file has the numbers coloured for my use, but it's all in mono here.

So, What SCR Generation and Software is Installed on a Car?

The configuration of a Mercedes that has been recorded correctly is stored in the Mercedes on-line system datacard for the vehicle – referenced by its VIN. Ensuring that the data correctly reflects the physical state of the vehicle helps ensure that the correct parts and work specification data etc. are linked to the vehicle. Any Independent or main dealer with on-line access to Xentry can access the very latest datacard on Mercedes’ system and take a copy of it for reference. If they are willing, you might get a copy from them.

Available for free on the internet is a site called ‘LASTVIN’ (search for it) where you can enter a VIN and get a copy of a vehicle’s configuration SA codes. If you do this you can check for the codes detailed below to see how your (or a prospective purchase) vehicle is configured. – Note that I don’t believe this database is linked directly to the Mercedes datacard and have noted that it is not always 100% up to date. I have no idea how often they update their database.

The infamous Diesel Software Update recall applies to code U42 and U77 vehicles and this updates software on the Engine, Gearbox and SCR system ECUs. This update is effected without adding any additional SA Code, so to check if this has been done you have to go to Mercedes’ site and enter the VIN there (search for the site and Diesel Software update recall). Note that I am aware that there are some U42 and U77 vehicles that have NOT had the Diesel Software Update recall installed. Such U42 and U77 vehicles should still be OK with original non-TT3 sensors.

Personally, I would check that any prospective purchase of a U42 or U77 vehicle must also have a code 30o or 03o. U79 is probably as good as it gets with SCR for now (May 2024).

BlueTEC (SCR) Relevant Codes

Code U42 - Diesel Exhaust Treatment BlueTEC SCR Generation 1

Code U77 - Diesel Exhaust Treatment BlueTEC SCR Generation 2

Code U79 - Diesel Exhaust Treatment BlueTEC SCR Generation 3

Code 121 – Control Code for NOx TT3 Sensor Slow – Software update/s and new TT3 Sensors

Code 30o – Conversion NOx TT3 Sensor Slow – Software update/s and new TT3 Sensors

Code 03o – Retrofitting Diesel (ZPD) – Engine ECU Software Data update and new front TT3 sensor

Notes on Numbers and Types of NOx Sensors Used on Mercedes – Taken from a Working Document (continually under revision and likely to contain inaccuracies)

This document includes details of the NOx sensors taken from ‘TT3.INI file dated 28/04/2023’ and used by Xentry 6/2023 version for checking software and NOx sensor compatibility. Sensors are manufactured by Continental. Vitesco is part of the Continental group and now sell directly to the after market – i.e. Not in a Mercedes cardboard box that costs £100s.

These are all ‘SMART’ sensors comprising an Electronic Control Unit (ECU) and sensor probe (NGK NS11A) ‘hard-wired’ together. Although the ECUs and probes may have evolved a bit, it’s the factory internal programming and calibrations that are the main differences. Some Vitesco part numbers are identical for different Mercedes part numbers and (probably) in most cases the sensors with longer cables will work OK in place of the equivalents with shorter cables. These NOx sensor ECUs can be ‘read’ digitally, but I have not managed to find any ODX database files for them for ‘proper’ interrogation.

The cable length, as far as is known, is indicated after the part number in the format Lxxx, e.g. L415 for 415mm.

Note that retrofit codes 121 and 30o ARE (or WERE if code 03o now supersedes them) applicable to ALL BlueTEC vehicles with Gen 1 and Gen 2 SCR systems. Gen 3 SCR systems are assumed to be already ‘upgraded’ at the factory as they have TT3-compatible sensors fitted??? The details below are notes made on particular models during investigations, but do NOT include every model looked at. Many models use the same sensors but the numbers and types of sensors fitted will vary dependant on the age and version of the model. The CLS models only exist in a few versions and the number of sensor possibilities is limited.

All NON-TT3 NOx sensors – NOT compatible with retrofit codes 121 and 30o. For retrofit code 03o (Retrofitting Diesel [ZPD]) fit to FRONT only.

A0009053403 L415, - Original factory fitted pair fitted to 2014 CLS 350 BlueTEC. Fitted to CLS FRONT as part of retrofit 03o. Also supersedes A0009056900 for GLK 220 and E 350 BlueTEC.
A0009053503 L615, - Supersedes A0009057000 for GLE 350 BlueTEC. Also originals for GL/GLS 350.
A0009053603 L815, - Supersedes A0009057100 for ML 350 BlueTEC and S350 BlueTEC.
A0035428818 L615,
A0065420918 L815,
A0065427218 L615,
A0009052800 L815, - Originals Fitted to ML 350 BlueTEC.
A0009052900 L815, - Supersedes A0009052800. Original front fitted to S350 BlueTEC.
A0009053000 L615, - Originals Fitted to GLE 350 BlueTEC. Also quoted as suitable by EPC for S350 BlueTEC.
A0009055100 L415,
A0009056900 L415, - Originals Fitted to GLK 220 BlueTEC and E Class 350 BlueTEC – Note that EPC data shows 615mm versions are OK for E Class both front and rear as well.
A0009057000 L615, - Supersedes A0009053000
A0009057100 L815 - Supersedes A0009052900

Note that A0009053503 and A0009053603 just have longer cables than A000905403. A0009055100 and A0009056900 are listed in the latest (03/2024) Vitesco catalogue as exactly the same sensors as A0009053403. Vitesco part number 5WK9 6681D for all three 415mm sensors (note this was 5WK9 6681C on the original factory fitted sensors removed from 2014 CLS).

All TT3 NOx sensors – Classed as ‘TT3 SLOW’ - Compatible with retrofit codes 121 and 30o. For retrofit code 03o (Retrofitting Diesel (ZPD)) fit to REAR only.

A0009053506 L415, - In 2021 a pair of these with Code 30o retrofit would have been the ‘fix’ for the CLS 350 BlueTEC AND E 350 BlueTEC. AND REAR of CLS 220.
A0009053606 L615, - This is the codes 121 and 30o TT3 sensor for a FRONT GLE 350 BlueTEC AND GL/GLS 350 AND also S350 BlueTEC.
A0009053706 L815, - This is the codes 121 and 30o TT3 sensor for a ML 350 BlueTEC AND S350 BlueTEC AND S 300 BlueTEC Hybrid. AND FRONT of CLS 220. AND REAR of GLE 350.
A0009055006 L415, - This is noted to supersede A0009053506 for GLK 220 BlueTEC.
A0009055106 L615,
A0009055206 L815,
A0009051412 L415, - Fitted to CLS REAR ONLY as part of retrofit code 03o. This number is specified as superseding A0009053506 and A0009055006 in Mercedes EPC (March 2024).
A0009051512 L615,
A0009051612 L815

Note that A0009053506 is/was the correct TT3 compatible NOx sensor for the CLS with codes 121 or 30o, front and rear at 415mm. A0009055006 and A0009051412 are suitable and form part of the supersession chain. In fact, all nine of these sensors would work, but the six in purple have incorrect cable lengths. Vitesco part numbers are: 5WK96681F for A0009053506 (no longer manufactured); A3C00311900-297 for A0009055006 (no longer manufactured); and, A3C03398500-620 for A0009051412. Not sure why the Vitesco part numbers are so different.

All TT3 FAST NOx Sensors – These are NOT compatible with the Gen 1 and 2 SCR code 121 and 30o TT3 SLOW retrofits. Looks like they are used on Gen 3 SCR models.

A0009050008 L415, - Valid for REAR of S 300 BlueTEC Hybrid chassis A from 14/03/2017 – Earlier models use the same Non-TT3 sensors as the CLS. If code 30o is fitted it’s the same as CLS.
A0009050108 L615, - Valid for FRONT of GL/GLS 350 BlueTEC USA and Canada Version models – NOT VALID FOR CODES 121 and 30o
A0009050208 L815, - Valid for FRONT of S 300 BlueTEC Hybrid chassis A from 14/03/2017 – Earlier models use the 815mm Non-TT3 sensors. If code 30o is fitted it’s the 815mm TT3 sensors.
A0009052709,
A0009052809,
A0009052909,
A0009053009, - Valid for FRONT of 213 (E Class) 220 Generation 3 SCR model. Also FRONT of 238 (E Class 220 D) model up to 12/12/2018.
A0009053109, - Valid for REAR of 238 (E Class 220 D) Generation 3 SCR model up to 12/12/2018.
A0009053309,
A0009053707,
A0009054604, - Valid for REAR of 213 (E Class) 220 Generation 3 SCR model up to 02/06/2016.
A0009054704,
A0009057108,
A0009057208,
A0009057408,
A0009059603,
A0009059703, - Valid for GL/GLS 350 BlueTEC USA and Canada Version models – NOT VALID FOR CODES 121 and 30o.
A0009059803 L815, - Valid for REAR of GL/GLS 350 BlueTEC USA and Canada Version models – NOT VALID FOR CODES 121 and 30o.
A0009053209
A0009055612,
A0009055712,
A0009055812,
A0009057308,
A0009058011,
A0009058111,
A0009058211,
A0009058311,
A0009058411,
A0009058511,
A0009058611,
A0009057803,
A0009055311,
A0009055611

All NOx Sensors for Petrol Engines

A0009056104 L415
A0009056204 L615,
A0009056304 L815,
A0009053803 L415,
A0009053903 L615,
A0009054003 L815

Best Regards:

 

[EdPhil]

A Quick Note as I just spotted an error in the previous post.

Code 03o on my CLS fitted a non-TT3 sensor (original factory number) to the Front and a new number TT3 sensor to the Rear.

I believe in one case I said the TT3 sensor was at the Front. - Confusion existed at one time as the garage originally did fit it there and it was only after I took the vehicle back home and checked it all through and against Mercedes current data for my CLS with code 03o fitted that the error was realised and corrected. I have many working documents on my investigations and don't always update the older ones as new information is uncovered.

Apologies.

 

[Beastlee]

Took mine in a couple of weeks ago for poor start and random terrible economy, no EML. They changed a pipe near the air box and one of the NOx sensors. No change to the car though.

 

[GrizzStudio]

Contacted MB UK HQ today, and waiting for a call back from the dept ( yes, they have a dept) that deals with emission complaints

 

[Seanalf]

This thread is incredible! Some great info in there. I'm thinking of changing my 2012 C-Class next yuear and the Nox issue had me looking away from Merc I'll be honest. So from what I can glean, I'd need to find a car that has Gen 3 sensors to have the best chance and these are fitted potentially from 2017 on?

Also, Iv'e been reading about people using a Wynne's additive for the Ad-Blue tanks to prevent crystalisation? Has anyone any evidence that it's not hocum and worth doing? I get you don't want to fill the tank, but what's the rule of thumb here?

 

[OneForTheRoad]

This thread is incredible! Some great info in there. I'm thinking of changing my 2012 C-Class next yuear and the Nox issue had me looking away from Merc I'll be honest. So from what I can glean, I'd need to find a car that has Gen 3 sensors to have the best chance and these are fitted potentially from 2017 on?

Also, Iv'e been reading about people using a Wynne's additive for the Ad-Blue tanks to prevent crystalisation? Has anyone any evidence that it's not hocum and worth doing? I get you don't want to fill the tank, but what's the rule of thumb here?

Upto gen 6 now maybe higher? Adding anti crystal is like descaling a kettle , even more so , it's like preventing a kettle from scaling up. Ad blue tank is imho best filled to the brim in the winter along with 250 MLS of anti crystal. This helps with freezing and keeping the system clean. Ever since the birth of ad blue I think mb have been guessing and correcting rubbish parts and software, maybe now in 2025 , they may of got it right ??

 

[Seanalf]

Upto gen 6 now maybe higher? Adding anti crystal is like descaling a kettle , even more so , it's like preventing a kettle from scaling up. Ad blue tank is imho best filled to the brim in the winter along with 250 MLS of anti crystal. This helps with freezing and keeping the system clean. Ever since the birth of ad blue I think mb have been guessing and correcting rubbish parts and software, maybe now in 2025 , they may of got it right ??

Nice one, thank you! I can't stretch to a new one, I think I'll have a budget of around £15k, saw a very nice C-Class Coupe for that, 2018 year. At least thsat puts my mind at reast a bit then. If I wait another year, who knows!

Good tips on the Ad Blue, I don't think that's wide knowledge

 

[OneForTheRoad]

Nice one, thank you! I can't stretch to a new one, I think I'll have a budget of around £15k, saw a very nice C-Class Coupe for that, 2018 year. At least thsat puts my mind at reast a bit then. If I wait another year, who knows!

Good tips on the Ad Blue, I don't think that's wide knowledge

My next will be an e300 or e450 petrol . If I had an older ad blue car , I'd pay £300 and have it deleted anyways . Upto now I've got a warranty still valid and I've had 7 free years of issues on 2 models . E350 16/17 reg coupe and e350 glc coupe 18/19 reg.