i thought the warning for fuel was when you got down to the last 7litres of juice?
i get a warning sound and a little light appears when i'm just about empty.
best bet is to nip down to lcoal VW dealer and one ofthe guys will probably sort you out in a jiffy.
they do something like turn the ignition on (not the engine) while holding in one of the buttons on the dash (i think its the mile-ometer) for a few seconds, mnaybe 4 or more seconds. That'll probably get rid of the service warning.