The fuel gauge starting to only read 1/2 full after filling it. After a few fill ups, the fuel gauge stayed on empty. Shortly after that I got an error code on the dash. I can't remember what the code was. I lifted the cab, pulled the sending unit out of the tank (4 Phillips screws and two wires. The unit looked clean except for a few rust spots. I cleaned the complete unit off with a tooth brush and RD-90. Then I checked the sending unit with an ohm meter. It seemed to be working properly, so I reinstalled it. It has worked fine after that. Good luck and stay safe.