I've ordered a fuso diagnostic tool, I am sure it will serve me well in my travels as well as tracking down the current derate problem. Being so reliant on being within range of a fuso dealer for access to a fuso specific diagnostic tool to even clear basic codes doesn't seem prudent in expedition traveling.
Out of interest Lehel, did you not consider trying one of the Chinese MUTIII clones? These units are still expensive, running in at around $500, but that is significantly less than a genuine MUTIII device.
I can not speak from experience, nor have I been able to find anyone that has one of these clone devices, but they are meant to be able to do "most" of what the genuine tool can do.
Probably a bit late now, if you have already ordered a genuine tool, but I would be very interested if anyone else has tried one of these clones, as I too am looking for something that can read/erase the codes from my Fuso (although, I do have the option of doing this via the fuse panel).