Hello & Welcome,
Can you tell us the Year, Make, and Model of your vehicle?
Can you give us a little more details also?
Is the gauge stuck at empty or full? Does it jump around?
The most common cause of this problem is a bad fuel level sensor. Below is the schematic that shows where it fits in the system. Note: The schematic shows two sensors, but you will only have one, based on what engine you have.
What typically happens is that the little metal 'fingers' that are used in the sensor, which are very thin, will break off and will cause an OPEN circuit back to the PCM (computer). As the schematic shows, anything over 250 ohms will show Empty on the gauge.
This sensor is mounted on the fuel sender assembly (fuel pump) in the gas tank.
To repair it, the fuel tank will have to be removed and the sensor, or the entire sender assembly will have to be replaced. What I would do is check on the price of the sensor along and compare it to the entire assembly price. If they are not too much difference in price, I would just replace the whole assembly.
I hope this helps. Please let me know what you find or if you have more questions.
Take Care, Greg A.