There’s a brilliant free mag that you can pick up in some parts factors... it’s called “professional motor mechanic”. Mostly has articles on new parts suppliers, updates and improvements to existing stuff and info on new ranges of spares coming to the market re complex systems that are becoming more and more popular. The other bit it does is have a deep dive into to the odd nasty surprise tripping up many garages. Often covers weird electrical faults. I remember one about Seat with a misfire and it was a failing ECU the diagnostics couldn’t pick up. Anyway back to Mercedes.... Now thinking as I write this.... it sounds very much like the article is trying to highlight Mercedes now deliberately build in fake faults that will get you an MOT failure. Yet outside the dealer network it will never get fixed and is only there to discredit independent garages and push an owner back in to the main dealership network. Funny that, as writing this I remember a guy at work having the VERY same issue impact a Vauxhall Mokka’s and CAT sensor faults no one can resolve.... The mag doesn’t quite say its deliberate fake faults being engineered into cars. But the fix is a great example of how your ave indy is never going to know about or be able to resolve. You get a real fault code on diagnostics, you can measure a real fault with the offending sensor and you can buy a genuine new sensor and correctly replace it. But still have the same issue ongoing. On the E class 2015 EML light comes on but the car drives OK, however diagnostic show P22AA heater circuit failure on the CAT sensor . The article goes on to say Merc have never even released a TIPS document re the issue and the part man will ALWAYS sell you the wrong spare part. The first part of the fix is to retrofit "special equipment code 30o" via online dealer tools. This updates the vehicle record so the parts EPC will now sell you the correct “updated spares”, you then replace both CAT sensors, reset adaptions on the SCR, then need to flash the Engine, Gearbox and Selective Catalytic Reduction (SCR) modules and clear stored codes. Funny as I write more points come to the fore about conspiracies... Recently we've had a sudden recall to flash many Merc ECU because "the EML light might come on". I suspect the EU got wind of the fun above.... and instead of buying two CAT sensors and giving Mercedes 500 quid... they've been told to take the trick out of the system "NOW !"