What is a fuel level sending unit?
The fuel level sending unit is located in the fuel tank, and sends a constant signal indicating the amount of fuel that remains in a fuel tank.

How does the fuel level sending unit work?
In most systems, the fuel level sensor will have a mechanical arm extending to the top of the fuel inside the tank. It will float on the top of the fuel, and as the arm moves down, the signal strength from the sending unit decreases. That information is eventually sent to the fuel level gauge for driver awareness. When the arm gets low enough, the light on the dashboard will be turned on, alerting the driver to stop for fuel.
What are the symptoms related to a bad fuel level sending unit?
When the fuel level sending unit fails, the fuel gauge will fail to operate, and, in some vehicles, the check engine light may illuminate. The on-board diagnostic (OBD) trouble codes stored will be relative to the fuel level sensor if the check engine light does illuminate. As no other symptoms rely on the fuel tank level, no other symptoms are expected.
Can I drive with a fuel level sending unit problem?
The vehicle can be driven without the fuel gauge. Most people use the trip meter and fill up the gas tank every time they reach their prefered mileage. The biggest risk is carrying gasoline or diesel fuel inside of the vehicle, or in the trunk. If gasoline is carried in case you run out, it must be outside the vehicle. The fumes inside the vehicle can cause injury and death.