As above i got a drivetrain error and limp mode last week.
Bit of a panic, but then it just cleared after 30 seconds or so.
Ok i thought keep going. Then it came back and went again a few times. This coincided with me having a failed flash on BM3 last week so i assumed these may be linked... Got it home and plugged it in to ISTA and saw 2 faults related to the Auxiliary water pump for charge cooler.
I don't want to take it to BMW or they'll update the car and I'll lose OBD access so i decided to fix it myself.. ISTA gives diagnostic steps and pictures for each fault code so i checked fuses etc jacked the car up and dropped the front undertray to get access to the pump.
Step 1 is check connector and supplies. If that doesn't fix it, it says to replace the pump!
The 3 wire connector was wet and dirty, (it sits right above the front oil cooler rad) checked for supply and ground all good. Cleaned the plug with alcohol, dried it then squeezed it full of silicon grease and plugged it back in.
But i then noticed the short wire loom to the pump was chaffed through the wrap and through the blue wire (LIN bus) insulation and copper was exposed. This was where it rubbed on the top of the ally front subframe squashed by the rest of the main loom tubing.. So as it touched the ally the signal from the pump would be lost. If this happens for more than 30 seconds you get the drivetrain fault.
So... I repaired the wire, taped it up and put sticky foam over the edge of the subframe to cushion the loom.
Fault cleared. Nothing more yet.
This is a common manufacturing defect for sure, something to watch out for if you have aux water pump faults...