* Fuel Level Sending Unit: This is the most common cause. The sending unit is located in the fuel tank and measures the fuel level. It might be faulty, corroded, or its float could be stuck. This is often the first thing a mechanic would check.
* Wiring Issues: A break, short, or corrosion in the wiring between the sending unit and the gauge cluster could lead to an inaccurate reading or no reading at all. Check for any damage or corrosion to the wiring harness.
* Gauge Cluster: The gauge itself could be malfunctioning. While less common, it's possible the gauge needle is stuck or the internal components are failing.
* Ground Connection: A poor ground connection can disrupt the electrical signal to the gauge. Check the ground connections related to the fuel gauge system.
* Fuel Pump Relay (less likely): While you say the fuel pump is fine, a problem with the relay could still impact the gauge's signal, even if the pump runs. This is less likely if the pump is definitely working.
Troubleshooting Steps (in order of likelihood):
1. Check the Fuel Level Visually: The most basic step. Try to visually determine how much fuel is actually in the tank. This helps eliminate the possibility of a truly empty tank.
2. Inspect the Sending Unit (requires tank removal or dropping): This is often the most difficult but frequently the source of the problem. You may need a repair manual for proper procedures.
3. Check the Wiring: Carefully inspect the wiring harness from the sending unit to the gauge cluster for any breaks, shorts, or corrosion.
4. Check Ground Connections: Ensure all ground connections in the fuel gauge circuit are clean and secure.
5. Test the Gauge (advanced): This requires a multimeter to test the gauge's resistance across different fuel levels simulated by the sending unit (if you can access the connector).
6. Consider a professional: If you're uncomfortable working on your vehicle's electrical system or fuel tank, it's best to take it to a qualified mechanic for diagnosis and repair.
Remember to disconnect the negative battery terminal before working on any electrical components. Safety first!
