Hooligan

So my misses Audi is causing problems We bought the car second hand and the steering rack went one day. Steering wheel extremely hard to move and red steering wheel on dash, Audi A3 2004 1.9TDI We had a friend look at it and he ran a diagnostic on it the problem was the steering rack. We bought a second hand steering rack and he fitted it without any issues. But... This second hand rack seems to be rejecting any coding that he tries to do. Please help