Double Dark Side! Diesel & 8P
Have you looked at this yet?:
I did a bit of reading up on this sensor a few months back when my ABS/ESP lights were on constantly. I had a faulty wheel speed sensor but if I remember correctly the steering angle sensors are in the cockpit of the car. One on the steering column somewhere and one accessable through the glove box.
Do a search in the S3 8L forum as it was mentioned a lot in there.
Hope that helps.