Hey okie I had the same problem with my 01 Impala as well. There is actually a really easy free fix that you can do. It most likely is the sending unit that is causing the problem. However, you DON'T need to replace anything!! Here's how the system works:
In the sending unit there is are feelers that make contact with a circuit board. Your car measures the resistance based on the position of the feelers on the board, and use it to display your fuel level. What happens over time is the feelers get worn out, and eventually loose contact with the board which cause your fuel gauge to go crazy. The easiest fix is to bend the feeler back towards the circuit board. I did this on my Impala and it works just as accurately and well as did before.
Here's the fix:
Thankfully GM has changed the design to allow you to get to the fuel pump without dropping the tank out. Fold the back seats down all the way and slide the carpet out of the way. This will give you access to a plate that is held in with a few screws. Take the plate off giving you access to the fuel pump.
There is a circular metal collar that with a gentle tap from a hammer and screwdriver will turn to allow you to pull the fuel pump assembly out of the tank. If I remember correctly, you have to remove the fuel lines and a wire harness as well.
Now you can pull the entire pump assembly out of the tank. There is a float attached to a piece of plastic. This is the area of focus. You can pull the plastic piece that the float is attached to off, giving you access to the little feeler. CAREFULLY bend the feeler so that it can make firm contact with the circuit board. Put everything back together, and you should be good as new.
You can also reattach the wiring and fuel lines to make sure the fix worked as you move the float up and down.
Altogether it takes about 30 minutes and doesn't cost a dime unless you break something along the way. There is a really helpful website with pictures, but I can't seem to find it at the moment.
Hope this helps
Last edited by tobinator23; 11-04-2010 at 11:41 AM.