Q: My fuel tank gauge always shows I have a full tank. What causes this and is it expensive to repair? I have a 1997 Buick Century. I have about 85,000 miles on my car. Maddy Leckey
A: Inside the fuel tank, there is a float attached to the fuel pump. As the fuel level goes up and down, so does the float. As the float moves it sends a signal to the gage in the dash that indicates the fuel level. The float is connected to a resistor and if it goes bad you will get false readings on the gauge. Another possible cause is a bad fuel gauge in the dash. However, the most common problem is the sending unit in the tank. On your model vehicle, the float, resistor and fuel pump are all one unit (called a fuel pump module assembly) and have to be replaced as one unit. The average cost to replace the unit is around $700-$800 for the repair. Due to the potential expense, I would recommend having the system diagnosed to determine which of the two parts are in fact bad and eliminate the risk of replacing the wrong part.