I did have to have the turbo actuator replaced on my old 2015 tfsi at the end of last year, I was getting a P334B fault code which is for a sticking turbo activator, a know fault on the TFSi engine, not sure if the diesel is the same. I had mine replaced under an extended warranty by Audi, they told me the cost would normally be about £400, or if the whole turbo needed replacing about £1500. I had the job done, but ended up buying the fully loaded 70 plate A3 Sport s-tronic they lent me!