I got my 2005 Audi A6 like 2 years ago and I didn’t know till I filled the gas up that it doesn’t go over 3/4 I could put in 4 gallons and it’ll go all the way to 3/4 I can also put 20 gallons and it’ll be at 3/4 till it goes down to less then 4 gallons If I put 2 gallons it’ll go up around 1/4-1/2 Any idea what’s wrong?