Simple/Easy Checks:
* Faulty Fuel Gauge Sender Unit: This is the most common culprit. The sender unit is located in the fuel tank and measures the fuel level. A malfunctioning sender can send an incorrect signal, indicating a full tank even when it's not. This often involves a faulty float or a corroded connection.
* Bad Fuel Gauge Cluster: The gauge itself in the instrument panel might be faulty. While less common than a bad sender, it's possible the gauge is malfunctioning and not accurately displaying the information it receives.
* Loose or Corroded Connections: Check the wiring connections to the fuel sender unit (within the tank; requires tank removal usually) and at the gauge cluster. Corrosion or loose connections can interrupt the signal.
More Complex Issues:
* Wiring Problem: A break or short circuit in the wiring between the fuel sender unit and the instrument cluster could interrupt the correct signal. This requires tracing the wiring harness.
* Fuel Pump Relay Issues: While less likely to cause a *stuck full* gauge, a malfunctioning fuel pump relay *could* indirectly affect the gauge reading if the system is improperly interpreting the lack of fuel pump activity.
Troubleshooting Steps:
1. Check the fuel level visually: The most basic check. If the tank is nearly empty and the gauge shows full, you've narrowed it down to a gauge or sender issue.
2. Check the fuel pump: Listen for the fuel pump when you turn the ignition key to "on." If you don't hear the hum, it could indicate an electrical problem, but it is not the main cause of this particular symptom.
3. Have a mechanic check the fuel gauge sender unit: This typically requires dropping the fuel tank, a job best left to a mechanic unless you're experienced with car repair.
4. Have a mechanic check the wiring: Tracing the wiring is tedious and requires specialized tools and knowledge.
5. Have a mechanic check the instrument cluster: This is usually the last resort as it may require significant repair or replacement of the entire gauge cluster.
Important Note: Driving with an inaccurate fuel gauge is risky. You could run out of gas unexpectedly. It's best to monitor your mileage and fill up more frequently than usual until the problem is diagnosed and fixed.
