On the page of the manual with the 'Replacing Toothed Belt' section, is a section for Replacing Reductant (Adblue). It says: Vehicle: All Audi Models Engine Versions: TDI Interval: 4 years (Reductant does not have to be changed if it was topped up within the specified interval) I know a bit about Adblue from working at JCB as some of the Tier 4 emission machines need it, but I didn't realise our Audi's used the stuff. Does anyone know where it's stored and how do you know if it needs topping up? The machines at work use gallons of the stuff, but I imagine the TDI engine in the Audi only uses a minute amount, but either way it'd be nice to know if it is used and where the tank is for it. Anyone come across this?