I recently changed the thermostat on my 2003 B6 A4 and after I was finished putting everything back together, the cars gasoline gauge is not working. It says the tank is empty and shows 0 miles. I know it was full with 3/4 tank. any suggentions?

 

Has nothing to do with the thermostat, have the fault codes checked, one of your fuel senders probably took a crap.