Fuel gauge problems are commonly the result of faulty electrical grounding at the tank or a problem with the sending unit inside the tank but can also be caused by faulty wiring or a bad fuse. Troubleshooting the problem involves a process of elimination that includes each of these as a possible root cause.
Vehicles running on ethanol-based fuel can be particularly susceptible to problems with the sending unit when they were not designed originally to operate with ethanol-based fuel. The alcohol content of ethanol fuel is such that corrosion of the wiring within the sending unit is common. If this is the cause of a fuel gauge failure, it can be resolved by removing and replacing the faulty component. Wiring from the fuel tank may also have become worn with time, a grounding wire may have become loose or a connection within the vehicle's electrical system may have been damaged.
Finally, the gauge itself may have developed a fault, preventing it from accurately displaying information from the sending unit in the tank. Vehicle owners should start by checking for corrosion on accessible electrical connections and evaluating the state of fuses within the vehicle's electrical distribution system. Unfortunately, replacing the sending unit within the tank often compromises the fuel tank, allowing vapor to escape.