Great guide to the BMW MOST Bus (Media Oriented Systems Transport), used in all BMWs with fibre-optic connectivity. It covers what it is and what it does, as well as troubleshooting a lot of associated problems with these complex systems. It is from Vlad at MCA.org and can be found here:
https://mca.electricmura.ro/en/blog-bmw-most-troubleshoot/
Been getting the 'Drivetrain' malfunction message on my F10 530d iDrive and figured it likely to be EGR (exhaust-gas-recirculator) related, so plugged in a Snap-On Modis scanner and these are the codes I got, which are what I suspected to be honest. The EGR and EGR-cooler are known to pack in on the N57 series of engine, the latter of which can leak coolant into the inlet causing a bit of smoke on startup.
28E200 - Exhaust Gas Temperature sensor before Cat, open circuit
255C00 - EGR Controller, Position Control, Valve open too far
190900 - EGR Mass Air Flow, measured plausibility calculated too high
240400 - EGR Control, control deviation air mass too low
272F09 - EGR, mechanically faulty close to open position
272E00 - EGR, mechanically faulty close to closed position
So, I have the classic two codes of the EGR failing close to open and closed position, which denotes a stuck EGR valve, which is quite common on all diesel engines, along with the EGR mass-air codes where values are higher and lower than they should be, which clearly ties in to the valve sticking in the open and closed position. Faults for the EGR control-module show that it is struggling to position the EGR correctly and this all points to one stuck EGR valve.
I also notice that I am getting a bit of smoke on startup sometimes which I have never noticed before. This also points to a faulty EGR-valve, or rather the cooler itself. The EGR-cooler is fed with coolant to reduce the operating temperature of the EGR-valve itself and these are known to have problems with leaking after time. They crack inside after prolonged use and start to leak coolant into the EGR and thereafter the air-intake, which causes a bit of white smoke on startup, which I have been experiencing the last few weeks and so it looks like this is the culprit and I will be replacing the EGR / cooler unit at some point I would imagine... watch this space.