I have a 99 a4 1.8t automatic 126000 miles

The gas gauge reads under full when filled completely. Also, when it gets under 1/2 a tank it flops between empty and the correct reading.

Does anyone know of this issue?

 

i have the same issue sometimes, iunno what it is either, sometimes it works perfectly, then sometimes it will stay stuck on full forever, then i run out of gas. Ill fill it up like, half way and it works normal again but sometimes it bounces up and down or not move at all. let me know if you get some answers on it.

 

there's a short to ground or a break in the short depending. the fuel gauge works on variable continuity. the fuller it is the less resistance to ground. your gauge may never go all the way to full. there is a few things coming in to play there and an old sending unit will probably have more resistance from corrosion and such.