F20 118i Drivetrain fault

So... yesterday afternoon the 118i decided to go into limp mode
Some drivetrain fault - called the dealer and advised that the car is operable but it's serious..

Yesterday evening I decided to check the car out again, it had since cooled down.. started just fine, fault was gone, boost was back and all seemed well and no warning lights were on..

Car was dropped off @ the dealer this morning and it's still there undergoing diagnostics..

My best guess: a faulty sensor/vanos/turbo?