* Faulty Fuel Level Sending Unit (float sensor): This is the most common culprit. The float inside the fuel tank can become stuck, corroded, or its arm can bend, preventing it from accurately reporting the fuel level. The resistance changes as the float moves, and if this is inconsistent, you'll get an erratic reading.
* Corrosion or Damaged Connections: Even if the wiring is fine elsewhere, corrosion at the connection points between the sending unit and the wiring harness, or within the sending unit itself, can interrupt the signal. Vibration can exacerbate this over time.
* Debris in the Fuel Tank: Debris in the fuel tank might interfere with the float's movement.
* Faulty Gauge Cluster: While less likely given the electrics check, a problem within the fuel gauge itself (though unlikely to be intermittent) is still possible.
* Wiring Harness Issues (despite previous check): While you say electrics have been checked, a problem could exist in a section of the wiring harness between the sending unit and the instrument cluster that wasn't thoroughly investigated. A subtle break or intermittent short could cause this.
Troubleshooting Steps:
1. Visual Inspection (if possible): If you can access the fuel pump area (often requires dropping the fuel tank, so caution and safety are paramount), visually inspect the fuel level sending unit and its connections for corrosion, damage, or debris.
2. Check Connections: Disconnecting and carefully cleaning all connection points (both at the sending unit and at any connector along the wiring harness) with electrical contact cleaner is crucial. Make sure the connections are secure.
3. Test the Sending Unit (if accessible): This requires a multimeter and knowledge of how to test resistance. The resistance should change predictably as you manually move the float arm. This is a more advanced step and may require a workshop manual to find the correct resistance values for your specific model. Incorrect resistance reading often points towards a bad sender unit.
4. Professional Diagnosis: If you're not comfortable with the above steps, taking your car to a qualified mechanic is the safest and most reliable option. They have the tools and expertise to diagnose the problem accurately.
Remember to disconnect the battery negative terminal before working near the fuel system to prevent sparks and potential fire hazards. Fuel is flammable, and working around it requires caution. If you're unsure about any step, consult a professional.
