I have a 2015 S5 that for some reason, the seat memory had a brain fart and had stopped working last week. The SET button would not light up and the high speed seat forward switch on the seat back had stopped working too. I found the solution in another Audi site but wanted to post it so it is easier to find. Here is what to do. Put the seat all the way forward (and hold for 5 seconds), full back (+5), full up (+5)and full down (+5). During each 5 second hold, there was a faint click (I think some motor drive relay resets). This simple procedure did it and all is good!