Fuel gauge reads backwards.

[ERIK RANGER]

Fuel gauge reads empty when full, full when empty. 1987 Ford Thunderbird Turbo coupe

Topic

[Richard Kirshy]

1. Fuel Gauge Sender Failure

More commonly known as a fuel sending unit, the component is what sends the fuel level signal to your dashboard indicator. While you are operating your vehicle, the sending unit is constantly in motion. This activity means it is rubbing against the variable resistor. The more you drive your vehicle, the move likely this friction will lead to an open or shorted circuit. When an open circuit occurs, the gas gauge may interpret the change in voltage from the failed sending unit as either full or empty. This is the most common reason why your gas gauge is reading wrong.
2. Circuit Problems

Circuit Problems – The gas gauge circuit is wiring that connects the gas gauge, sending unit, the battery, and a ground. The provides the power from the car to operate the electrical components of the vehicle. Because the gas gauge runs through this circuitry, if there is a problem such as a loose connection or corrosion within the circuit, this can cause an error with the gas gauge reading. If you feel comfortable under the hood, go ahead and check for loose or dirty wiring. Sometimes it’s the smallest thing causing a seemingly big problem. To learn more about circuitry, check out how car electrical systems work.
3. Fuel Gauge Is Faulty

Fuel Gauge is Faulty – This is less likely than the previous two issues. The gas gauge is the visual indicator between the fuel tank and the sending unit. In other words, it’s what you read inside the cabin of your vehicle telling you how much fuel you have. Typically, if there is an issue with the fuel gauge, there is a problem with receiving input from the sender. This could be from a bad ground or once again related to the circuitry. A proper diagnosis can help determine if this is the issue.
4. Instrument Cluster Failure

Instrument Cluster Failure – Instrument cluster is the industry’s way to essentially say dashboard indicators. This includes your fuel gauge, speedometer and so forth. With some luck, this will not be the issue. While it is the least likely cause your fuel gauge is reading incorrectly, it is the most expensive reason. Most newer vehicles have a fully-integrated instrument cluster meaning if one indicator has an issue, the whole unit needs to be replaced to fix the problem. Make sure to check out any warranties associated with your vehicle if this seems to be the problem.

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