Hyundai Repair: 2000 Elantra Fuel Gauge drops fast, fuel gauge, fuel sending unit

Question
My daughters 2000 Elantra's fuel gauge goes to full when she fills it but it drops to near empty after about 75 miles and stays there moving slowly to below empty for the remaining 225 or so miles.  Is the fuel sending unit under the rear seat somewhere and does it have a float that can be adjusted?  Any help will be greatly appreciated.   Thank you.    Paul

Answer
The problem is indeed most likely the fuel sender like you suspect.  Unfortunately, it's not adjustable.  It sounds like the sender unit's circuit board is faulty.

The sending unit is in the fuel tank, but you can access it through the access panel under the rear seat.  Once you've got the access panel loose, you can unbolt the fuel pump assembly, remove, and take the sender off of the fuel pump assembly.