So after nearly 12 months of pain I've finally got this working. For anyone following in my footsteps wanting to install a genuine retractable towbar here's how to do it. If you only want to perform coding for a removable towbar (using genuine Audi parts to connect to the CAN bus) then you can follow the subset of instructions below. Prerequisits - Audi A4 B9 (Allroad) - these come with tow prep - but for the life of me I've never been able to get Audi to explain what this means. - Audi A4 B9 - need to ensure that you have space in the well below the rear bumper for the towbar to fit and extend. The cut out is approx 30cm wide by 20cm deep - I believe that on A4 models it may require cutting the space in the bottom of the rear bumper. The position of the opening means that neither the opening nor the towbar can be see when it's retracted. - VCDS or VCP - if you are installing a removable towbar you can code it with VCDS alone. If you are installing a restractable towbar you can code it ith VCDS prodiving your tow controller has been parameterised. If not you need VCP so that you can parameterise it. This process takes 30 seconds and is a guided function within VCP so I'm happy to help people who need it. Parts - Genuine retractable towbar - Allroad 8W0800491N - B9 the last letter of the above part number changes depending on the model - you can find out from Audi what should fit your car.- Wiring loom, switch and controller: https://wibutec-shop.com/Kabelsatz-fuer-schwenkbare-Anhaengerkupplung-Audi-A4-8W - Tow Controller (I got mine direct from Audi so only bought the wiring loom from Wibutech) 4M0907383F (again the last digit of this seems to be different in different models.) - Tow bar release switch 8W0951511 (I also got this direct from Audi) - OR removable towbar https://wibutec-shop.com/Westfalia-Anhaengerkupplung-Anhaengezugvorrichtung-fuer-Audi-A4-B9 - Wiring loom and controller - 7 or 13 pin connector https://www.pfjones.co.uk/audi-a4-b...ds-13-pin-westfalia-dedicated-wiring-kit.html Installation The instructions from Wibutech are provided via PDF - they are 10Mb so I can't attach them here but can send them onto people that need them. Coding The Wibutech document contains the necessary coding instructions but here they are: Parameterising the Control Unit This is where I got stuck - I'd done all the above but the release button for my tow bar just refused to work. I tried changing the coding options in VCDS but it made no difference. If you're lucky your control unit may be parameterised already but it not you will need VCP to do this. I've attached a screen shot below but from the VCP file manager you download the ZDC file for the Audi A4 Tow Controller and then use the File Upload function to upload it to Module 69. The whole process took less than 30 seconds once I knew what to do and the button started working immediately. I now have VCDS and VCP if anyone in the Norfolk, UK area needs help with coding.