The most likely cause of a faulty gas gauge is a failing fuel level sending unit inside the gas tank. This component's variable resistor, often called a "float arm," changes its electrical signal as the fuel level rises and falls. When it wears out, it sends incorrect data to the gauge on your dashboard. Other common culprits include a blown fuse, a faulty instrument cluster gauge, or damaged wiring.
Before assuming the worst, check the simple stuff first. Locate your car's fuse box (consult your owner's manual for its location) and check if the fuse for the instrument cluster or fuel pump is intact. A visual inspection of the wiring running from the fuel tank to the front of the car for any obvious damage or corrosion can also reveal the issue.
If the fuse and wiring are good, the problem is likely the sending unit itself. Replacing it is a more advanced repair. It requires dropping the fuel tank or accessing it through an interior panel, which involves safely disconnecting the fuel lines and electrical connectors. Due to the safety risks of working with fuel systems, this job is often best left to a professional mechanic.
| Potential Cause | Symptom | Approximate Repair Cost (Parts & Labor) | DIY Difficulty |
|---|
| Blown Fuse | Gauge dead, doesn't move at all | $20 - $50 | Easy |
| Faulty Fuel Sending Unit | Gauge reads empty when full, fluctuates erratically | $300 - $800 | Hard |
| Bad Instrument Cluster Gauge | Gauge stuck, other gauges may also malfunction | $400 - $1000 | Moderate |
| Damaged Wiring | Intermittent or incorrect readings | $150 - $400 | Moderate |
