Stuck Fuel Sender
 

Just back from a couple of weeks with the S8 in Ireland Both ferriess I ended up on a downward slope and both times on leaving my half a tank of fuel suddenly turned into 0 miles range

In both case filling with fuel caused the gauge to gradually return to normal readings and in both cases she only took as much fuel as I'd expected (i.e nowhere near a full tank)


I conclude the cause is a stuck fuel float, anyway to prevent this from happening again as whilst ultimately an annoyance it was somewhat disconcerting

There are two fuel level senders. The left one is a conventional ball on a stick. The right one is float in a tube. The instrument cluster adds them both to get the overall level so I can't quite fathom how one of them would cause a zero reading. What I can't remember is which way the resistance goes for full / empty. It might be that open circuit is zero, and at a particular fuel level you have a bad contact on the sender. I think that is most likely to be the left one.

I'd try unplugging the left sender and see what the gauge does - its simple to get to, just three screws under the boot carpet to release the cover. If it reads zero when unplugged then open circuit somewhere, and I'd be inclined to replace the left sender unit first. If it doesn't read zero when unplugged then, er, something else...