My gas gage does not work. After I fill up with gas...withing 20-30 minutes it goes all the way down to empty. Should this be fixed or would it be too expensive to fix. The car is a 1999 Pontiac Grand Am GT

Either your gauge is bad or the fuel level sender is. Most likely it's the sender in the gas tank. To replace it you would have to drain the fuel tank and pull the fuel pump/sender assembly and replace. You cannot just replace the fuel level sender with this car, the entire assembly must be changed out.

Either you have a faulty fuel level sending unit or fuel gauge. The fuel level sensor is inside the gas tank and attached to the fuel pump. Cost usually $200-$330 to fix, depending on the repair shops hourly charge!!Hopefully this helpd