Fuel Sending Units and Switches
The fuel tank sending unit is a fuel level sensor located inside your gas tank that measures the amount of fuel in the tank, and communicates this information to the fuel gauge on your dashboard. Depending on your type of vehicle, the fuel sending unit can be a stand-alone unit, or may be attached to the fuel pump. Fuel sending units utilize a float attached to an arm that changes the position of an electrical resistor as the fuel level rises and falls in the tank. This change in electrical resistance is sent to your fuel gauge to be interpreted as the appropriate fuel level measurement. Some fuel sending units may also feature a secondary sensor that activates a low fuel light if fuel falls below a set level. If your fuel gauge is fluctuating, displaying inaccurate fuel levels, or not working at all, then you may have a failing fuel sending unit. Corrosion, wiring problems, a faulty resistor, or float arm mechanical failure can all cause issues with the fuel sending unit's accuracy and performance, so it may be a good idea to remove the fuel sending unit from the tank and inspect or test it before opting for replacement. Any time the fuel sending unit is removed from the tank, it is important to inspect and/or replace the gasket or sealing ring as well, as failure to do so may allow fuel vapor or liquid fuel to escape from the tank. It is also not uncommon for fuel sending unit floats to leak over the course of time, and this can allow the float to fill with fuel and sink to the bottom of the tank. If that is the case, it may be possible to simply replace the float. Testing the electrical resistance of the fuel sending unit with a multimeter can also help you determine if the problem is in the fuel sending unit itself, or if the fuel gauge, wiring, or a fuse or relay may be the source of the problem. If you need to replace a fuel system component, O'Reilly Auto Parts carries replacement fuel sending units and fuel pumps for most vehicles to help you complete your fuel system repair.
