The 1.8 t engines are prone to oil sludge build up which can cause a blockage to the pump which i suspect has happened to yours !! Have a read of this
http://www.audi-forums.com/b6-forum/...ure-light.html
Have you actually shelled out big money from Audi for a new lump then ? as i had the same problem which crumbled my piston and got a full engine rebuild for £1300 which was better than the £3500 Audi wanted..