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. In short, generation 1 and 2 SCR systems are a bit naff whilst generation 3 SCR is much better. What gen SCR your vehicle has fitted makes a difference and I suspect a lot of the people griping here and elsewhere don't know what gen they have fitted. A year and a half ago I didn't have a clue!
Note that I am just an 'owner', and my opinions are just what I have come to understand over time. I am happy to be wrong, but seen and heard nothing to convince me differently yet! In my case, I have mainly been posting under a 'Value 751' thread and have recently had my CLS 350 NOx sensor problems finally 'fixed' (I hope). - The full detail about all that will be posted under that thread later when I have run my car for another month or so, but here's a few 'snippets' that relate to aspects of your post that should be of interest. Apologies for not explaining all the abbreviations if you don't already know what they mean, but just know that Selective Catalytic Reduction (SCR) is effectively what BlueTEC is all about.
Firstly, if you have a 2017 213 E Class 220 D, it's most likely fitted with the Generation 3 SCR system, which 'fixed' most of the Gen 1 and Gen 2 NOx sensor issues caused by the Diesel Software Update - your car did not need the update. Your Nox sensor failure was possibly just a 'normal' failure (they do happen) and just required replacing with no other software mods. DTC 'P300646 Component NOx sensor downstream of SCR catalytic converter has a malfunction. The commanded position cannot be reached.' looks like a 'proper' failure, but I would have to do a bit of digging to find out exactly what the 'commanded position' is, and what the exact fault trigger parameters are.
Mercedes Xentry is a good tool, but my observation is that it's a GUI mostly about identifying parts to replace, not repair them. The two Xentry tests for the NOx sensors (control unit and probe) don't test the sensors at all. They just test that the voltage supply and CAN lines on the wiring to the control units meet certain resistance criteria. If the wiring checks out the process is to then to fit replacement sensor/s. A diagnostic scan for NOx sensor DTCs is therefore very limited in scope, takes about ten minutes and, as long as it's not badly siezed, it's usually less than an hour to replace one and retest. Obviously, there's the time for paperwork and admin to consider.
What caused/causes many confusion at this stage is that, although (leaving just cleaning aside) it could simply be a matter of replacing the NOx sensor with a new one, it depends on whether the vehicle also needs some software updates as well. Generally, the need to update software applies to ALL generation 1 and generation 2 SCR system vehicles that already had the Diesel Software Update applied and no other updates. Retrofit codes 121, 30o and 03o with software updates and appropriate NOx sensors are correct fixes for gen 1 and gen 2 vehicles. Only the garages (or someone) with on-line access can perform this properly and get the Mercedes vehicle datacard updated to reflect the retrofit code and correct EPC NOx sensor numbers.
To further confuse people, there are effectively four basic NOx sensor types that Mercedes use. These can simply be classed as 'Non-TT3', 'TT3', 'TT3 fast' and 'Petrol' - Diesel owners can forget the petrol engine sensors. As well as there being four basic types of NOx sensor, there are three cable lengths (415mm, 615mm and 815mm), and there are also several numbers for what are essentially the same thing due to manufacturing number changes and supersessions. Consequently, there are lots of different numbers in existence, but it's really only four basic types with three variations of cable length for each.
In general, non-TT3 sensors are the original type fitted to generation one and generation two SCR systems. A pair of these were (and still should be) OK with the factory installed vehicle engine ECU software, but one or both get 'stressed' with the Mercedes recall Diesel Software Update applied (this makes the system 'work' much harder than it was designed to) and can fail prematurely and/or generate erroneous readings that can cause misdiagnosis on other parts of the SCR system.
The proper 'fix' for gen 1 and gen 2 vehicles with the Diesel Software Update applied is/was to fit two new TT3 sensors (so the part numbers change) and update software under codes 121 and then 30o (superseded 121) retrofits.
A month ago I became aware that Mercedes have recently introduced a code '03o Retrofitting Diesel (ZPD)' retrofit for gen 1 and gen 2 vehicles, which updates the data settings software (not the programming) on the engine ECU only and uses a Non-TT3 sensor at the front and a TT3 sensor at the rear. This can be applied to a vehicle that has had the Diesel Software Update applied, but not codes 121 or 30o. Effectively, this means that only the rear sensor needs to be replaced if it's just that one generating faults. It's likely the code 03o retrofit is being enforced by Xentry now in place of code 30o.
Generation three SCR systems were 'fixed' with what was effectively a Diesel Software Update (as well as better hardware) before leaving the factory. I have checked a couple of these gen 3 vehicles, and they seem to use the TT3 fast sensors.
The latest sensor numbers likely to be fitted to a 213 E220D are A0009053009 Front and A0009053109 Rear - TT3 Fast sensors, but I suspect that the supply chain issues may have Mercedes offering alternatives as part of their 'supersession' chain.
Mercedes main dealers and independants with Merc subscriptions always seem to want to fit 'Mercedes boxed items' when there are sometimes perfectly good, same quality after market parts available. Quality (not the cheap Chinese versions) NOx sensors that Mercedes cannot get hold of from Continental/Vitesco are readily available elsewhere. Continental/Vitesco themselves supply to the after market now. The only bit you probably don't get is a very expensive Mercedes cardboard box for your recycling bin.
Mercedes charge about £600+ for a new NOx sensor, but they have managed to get supplies of some remanufactured (repaired) sensors and they sell these for about £400+ each. Looks like you got one of these fitted to your E220.
Mercedes main dealers and indys with subscriptions to the Mercedes on-line system tend to just follow what the system tells them to do. What they rarely, if ever, tell the customer is exactly what they did in detail and, in my experience, don't really test that what they have done with NOx sensors is working properly. That's due to the time it takes to get the NOx sensors working properly and some faults may reoccur several hundred miles later after a 'fix'. That said, I am pretty sure Mercedes have been modifying Xentry over recent years in an attempt to improve or tighten up NOx sensor matters.
Mercedes NOx sensors are manufactured by Continental/Vitesco and are self-diagnosing 'smart' sensors, factory programmed and calibrated. When one first powers up it basically just sends a signal saying 'Hello, I'm OK' (or not OK). So when the technician checks the newly fitted sensor, as long as it's the correct type of sensor for the SCR software, Xentry should report no errors and generally it's now invoice time. However, the SCR system does not become fully operational until the vehicle has been driven for quite some time and some faults are only flagged after a couple of drive cycles, so errors can occur some time after the repair if it was not the correct 'fix'. In my experience the garages do not do the road testing necessary to prove the sensors are functioning correctly, and I doubt that customers would be happy to pay for it anyway. During proper testing of fully operational sensors the live graphing of NOx level readings, adblue dosing etc. are all available to record and analyse. If the 'fix' worked, most people would see this as a waste of time and money. However, if the 'fix' did not work and the customer gets a MIL a short time afterwards, it's then a trip back to the garage and generally lots of moaning and complaints from the customer that aren't always justified.
There are also some very involved and time consuming processes that are often necessary to reset and relearn the SCR system. These, like the fact that you can't tell if the system is working properly until you have road tested the car for some time and checked the readings, don't seem to be at all well publicised. It's about ten minutes work to bypass the ECU security and reset/delete the AdBlue countdown if you have the correct software. However, there's other things you need to do as well and you might also have to run the vehicle for a considerable mileage up (e.g.) a motorway at a consistent speed to check and get the SCR system to reset correctly. It's not immediately apparent that these other processes are required and if they are not done faults are likely to come back again in the future.
Note that I have not been able to discover what 'TT3' or 'ZPD' actually means yet.
Finally, a Taxi Driver friend of mine has a late 2016 E220 gen 3 SCR and he's had no problems with it in over a year now since he bought it (lots of mileage). You probably won't get as many problems with your car as us old farts with gen 1 and gen 2 SCR systems - replaced by gen 3 mid 2016, I think.
I trust some of that is of interest and makes you feel a bit better than the tales of doom.
Best Regards.
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