Get your mate to get on here:
https://www.vwaudiforum.co.uk/
It's the one I used when I had the Passat. They have their version of Arctic - a guy called "Crasher" with just shy of 40K (yes, you did read that right
) posts.
The folks on that forum will be able to help. My first guess is he'll benefit from getting someone with VDCS (VW Diagnostic Computer System - I think). Think T4.
I found them to be a very friendly bunch.
Good luck.