It's designed for a B5/8D model...
http://www.a4-freunde.de/pdf/gra_b5_diesel.pdf
Edit

anything else for the B6?
http://a4.scirocco-5v-turbo.de/beschreibungen/gra/gra-nachruestung.html
Or simply search for it yourself...
zb www.a4-freunde.de or http://www.audi4ever.at/index1024.html
Hello friends,
Don't be discouraged if your workshop tells you that the retrofitting of a GRA (Gas Return Actuator) is not possible on the new A4, type 8E.
'is no longer possible!!!'
I had the GRA installed later, and it works perfectly!
I was fortunate enough to find a workshop foreman at VW Fuchs in Linz who was interested.
who, at my urging, also decided to tackle this topic!
The required parts are:
8E0953521D 4PK Cruise control switch.
8E0953549L Electronic module (Probably only required without a multifunction steering wheel and without a FIS - onboard computer).
8E0953512G 6PS Lower trim panel (pay attention to the color).
Everything is working great, including the display that lights up between the speedometer and tachometer when the GRA (gradient assistance) is activated!
According to the workshop, the only advice I can give is to have the diagnostic device tested beforehand.
ob sich die GRA-Funktion im Steuergerät wirklich freischalten läßt. Diese Vorsicht ist insofern geboten (lt. Weworkshop)
because the parts catalog specifically lists two part numbers for the control unit – one with GRA and one without GRA.
But, as you can see, I needed an engine control unit without GRA (Gasoline Direct Injection), but apparently, the function can still be enabled.
enable.
According to Meister, unlocking the feature in the diagnostic device's menu is just as easy as it is for, for example, a 1997 Golf TDI.
If your workshop can't find this menu item, then it's time to question their expertise!
Okay, friends of all GRA clubs – it's really about the new A4 – let's head to the workshops!