fault 171:12
control unit hardware fault
Internal temperature for control unit not in permissible range
does the fault clear when you shut down and restart?
the suggestion says to shut it down and restart it and it should start up normal but if problem reoccurs to call Deutz service.
It almost sounds like a faulty temp sensor or wiring.
Also check the fan belt and make sure it is not loose.
It doesn't specifically say but another possibility could be the engine controller is getting hot.
That's the trouble with the service literature, sometimes it isn't very specific.