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Diagnostics > By Symptom > Electrical symptoms > Fuel gauge not working

Fuel gauge not working

Fuel gauge not working or wrong

If your fuel gauge doesn’t work at all or is reporting the wrong fuel level, the problem is either a bad fuel sending unit or a wiring harness issue.

How the fuel gauge works

fuel sending unit versus fuel pump module

The fuel sending unit consists of a variable resistor, a flow and float arm. The fuel sending unit in fuel injected vehicle is built into the fuel pump module. The float rides on top of the fuel. As the fuel level changes, the float arm moves in the variable resistor changing the voltage. In older non-computerized vehicles, the sending unit is wired directly to the fuel gauge. However, in late model computerized vehicles, the fuel level signal goes to the body control module (BCM) which then sends a digital signal to the dash cluster.

Diagnose a fuel gauge not working or fuel gauge wrong issue

Using a shop manual, measure the reference voltage into the fuel level sending unit. Then measure the return voltage back to the gauge or BCM. Compare the return voltage to the expected voltage based on the amount of fuel in the tank. If the return voltage is off, chances are the variable resistor is corroded or the float level arm is bent.

If you’re not seeing the reference voltage, check for a wire harness issue.

Replace a fuel sending unit

Replacing a fuel sending unit is a pretty big job. In some vehicles, you can access the fuel sending unit and fuel pump module by removing an access panel under the rear seat. But in other vehicles you have to drain the fuel tank and then remove it from the vehicle.

The fuel pump module is held in place by a locking ring and some require a special tool to remove the ring. I recommend replacing the entire fuel pump module as opposed to replacing just the fuel sending unit.

 

© 2012 Rick Muscoplat

Posted on by Rick Muscoplat

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