Fuel gauge

What is the gauge doing? Usually it is a faulty fuel sending unit when the gas gauge is not reading the correct fuel level.

Is there any way of repairing the sending unit or is it a lost cause?

Please explain the symptoms. There are a number of common symptoms with very different causes, and some have simple fixes.

When I fill the tank the fuel gauge stays on empty
With about half a tank left the fuel gauge will begin working again

It sounds like a bad fuel sending unit with a full tank of gas try rocking the car while the car isn't moving and engine turned off with the key in the run position while watching the fuel gauge.See if the fuel gauge moves?

Yup. You may be able to fix the sending unit. This was a somewhat common problem on Chrysler minivans in the early to mid '90s. The symptom always was the gauge read correctly from "full" to "1/2" and from "1/4" to "empty", and it dropped to "empty" any time the level was between "1/4" and "1/2". The fix was to lift the fuel pump assembly part-way out of the tank, bend a small plastic finger to allow the float arm to be slid off, then bend the metal tab slightly on the arm so it made better contact. Pop the arm back on and put it all together. The factory-recommended repair was to replace the sending unit, but chances are it would develop the same problem in a few years.

Your sending unit has to be unbolted from the pump housing. Once removed, look for a moving contact that can be bent to put more pressure on it.

Being a 1999 I bet the fuel gauge is a pluse width modulated and the sending unit would be more of a circuit board requiring replacement.I remember when I worked for saturn we were issued a bulletin that was multi brand wide even toyota was listed on the buletine.It said 50 state wide the additives in the fuel were damaging the sending units.I would replace the fuel pump module that would come with a new fuel sending unit.Thats whatbd9 always do do people with the same issue.