A4 detailed workshop DIY manual

You should be looking for ElsaWin workshop manual from 2008-2015 (B8). This is what's supplied to the dealer network. Anything on Ebay is a copy and probably illegal. In addition, a genuine copy of VCDS software is I think essential given it can help pin-point faults. Change and reset the on board computer after oil service, even brakes, then you have electronic handbrake to release, priming diesel fuel-pump after changing, etc. Haynes do a diesel manual for your car. No idea how good it is though?

Haynes yes for some things, easymanuals.co.uk sell copies taken from Erwin, so they will probably only grab these manuals once in the lifetime of a model life, I've bought it for A4 B8 in DVD format and dumped everything that did not apply to my S4 and have it on a USB stick along with same for my wife's 2015 VW Polo 1.2TSI and my daughter's 2019 SEAT Leon Cupra.

30 euros gets you 24hr access to Erwin where you can download everything. It took me about 30mins max to get everything A4 related. All in PDF