* Faulty Fuel Level Sending Unit: This is the most common culprit. The sending unit is a float mechanism inside the fuel tank that sends a signal to the gauge indicating how much fuel is present. If the float is stuck, broken, or the sending unit itself is malfunctioning, it will consistently send a "full" signal regardless of the actual fuel level.
* Wiring Issues: A break, short, or corrosion in the wiring between the sending unit and the fuel gauge can also cause inaccurate readings. This is less likely than a faulty sending unit but still possible.
* Fuel Gauge Cluster Problem (Less Likely): While less probable, the fuel gauge itself within the instrument cluster could be malfunctioning. This is usually accompanied by other gauge issues.
* Rare Possibilities: Extremely rarely, a bad ground connection or even a PCM (Powertrain Control Module) problem could affect the gauge, but these are less likely scenarios.
What you should do:
1. Check the Fuel Sending Unit First: This is the most likely and easiest to check (though it requires some work). It's usually located inside the fuel tank. This job often involves dropping the fuel tank, which is moderately advanced DIY work. You'll need to be careful with fuel handling and potentially have access to a fuel pump removal tool. If you're not comfortable with this, take it to a mechanic. You may be able to find videos online showing the process for your specific car.
2. Inspect the Wiring: If replacing the sending unit doesn't fix it, then a visual inspection of the wiring harness leading from the sending unit to the fuel gauge should be done. Look for any damage, corrosion, or loose connections.
3. Professional Diagnosis: If you're not comfortable working on your car's fuel system, take it to a qualified mechanic for diagnosis and repair. They have the tools and expertise to properly diagnose the issue. They can also test the gauge itself with a scan tool to rule out other possibilities.
Important Safety Note: Working with the fuel system requires caution. Always disconnect the negative battery terminal before starting any work. Gasoline is highly flammable, so ensure good ventilation and avoid sparks or open flames.
Continuing to drive with a faulty gauge is risky because you could run out of fuel unexpectedly. Stick to your current practice of filling up frequently until the problem is resolved.
