diagnosis is easy on european cars as their service literature is thorough and deep level. The catch is that the literature assumes you are educated, understand machinery repair concepts, understand data networks and also low voltage networks.
With japanese repairs - its usually throw parts at it till its fixed.
e.g. layered build concept
this is the service position of audi - if you want to repair anything in the front of the engine.
it looks scary - but in reality its not, it takes about 30 minutes at max and the only special tool required is a refrigerant recovery unit - you put it back in after the service.
I once got a call from some audi owner in lahore whom I skyped with, he had a LHD turbo A6 - The owner never disclosed the workshop but on skyping he showed me that the shop had literally tore the engine to bits to take out the turbos.
The correct way was to remove the front, undo the wiring, drain and undo the coolant, disconnect from car, undo the suspension towers, undo steering, lower the powerpack complete and intact onto a table, remove and reinstall turbos and pack it back.
The shop took a week to tear it down and twice as much to pack it back. When it could have been done in a day if they followed audi procedure.