Gas gauge drops to E when you fill it. on 2009 Hyundai Santa Fe

1/8 tank, fill it completely, and the gas gauge drops to E and the low gas light comes on. Took 3 days for gauge to very slowly rise. Now it drops below E and the low gas light comes on when I start it and it should be full about 3/4 or more.......Very frustrating and the mechanic says they can't find anything wrong???????? HELP Please

Asked by for the 2009 Hyundai Santa Fe
sounds like your sending unit is screwing up
Thanks GoodGuy! I had it at the shop this week and they "hooked it up to the computer" and said everything was "ok"... yeah right...........I miss the days when mechanics actually found the problem......