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Fuel gauges are fairly simple mechanisms. They point to “E” when the tank is nearly empty and “F” when it’s full. At least, until it doesn’t. Then you’re left in the dark, guessing how many miles you can squeeze from the last remaining droplet of fuel before the car sputters to a halt along the side of the road. 

What people might not know is why and how that gauge goes up or down. It’s not a direct mechanical connection, it uses electricity to make it work. This setup can create some confusion as to what exactly is wrong when the fuel gauge starts malfunctioning. 

Still, with a little patience and a multimeter, the home mechanic can diagnose the problem at home with a little elbow grease and understanding of the wiring. The Drive’s editors want to equip you with the knowledge you need to get the job done so you don’t waste money paying the pros. 

Find your inner DIY spirit, and let’s get to it.

A car’s fuel gauge, whether digital or analog, informs the driver how much fuel is left in the tank.

The fuel gauge displays the information that is conveyed from the fuel sending unit, which is attached to/on/in the fuel tank. Based on that information, an analog gauge will move a needle up and down across a dial or a digital gauge will display a set number of bars that show how much fuel is left. When the tank switches to its reserves, it will prompt a fuel light to display.

The fuel sending unit has a float arm that sits in the liquid gas. When that arm moves up and down, it changes the resistance to ground on a variable resistor. That resistance is then translated and sent through the car’s wiring and electronics to determine where the needle or digital gauge is positioned. When the tank is full, it registers a high resistance, and when it’s low, it registers a low resistance.

If you notice these symptoms, you might have issues.

Use the process of elimination through testing to determine what your problem is.

Estimated Time Needed: Could be hours, depending on the location of and access to the fuel gauge sending unit.

You’ll be underneath the hood, testing electrical wiring,  and dealing with gasoline for this job. Make sure you prepare the proper safety equipment and precautions to ensure you leave the garage in one uninjured piece.

Organizing your tools and gear so everything is easily reachable will save precious minutes waiting for your handy-dandy child or four-legged helper to bring you the sandpaper or blowtorch. (You won't need a blowtorch for this job. You’re dealing with fuel and fire is bad when you add fuel. Please don’t have your kid hand you a blowtorch—Ed.)

You’ll also need a flat workspace, such as a garage floor, driveway, or street parking. Check your local laws to make sure you’re not violating any codes when using the street because we aren’t getting your ride out of the clink.

Now, let’s get to the step-by-step process of locating your problem.

Find the fuse for your fuel gauge and check its health. If it’s blown, replace it, and you might be in the clear. If your fuse is fine, or you’re still having problems after replacing it, you have a different issue.

Most modern cars built beyond the early 1990s have built-in testing procedures. They are typically activated using some combination of the light switch, the trip button, and other dashboard buttons. Check your owner’s manual for the specific code. If you run the check, and the needle circulates through its up and down motions, then the gauge is okay, and you have a problem elsewhere.

Learn how to use a multimeter to test your fuel gauge sending unit in the next section. These are general steps that might not apply exactly to your car, but it details the general process.

You’ve got questions, The Drive has answers!

A: We don’t recommend it. Without knowing how much fuel you have, you could not only end up in a perilous situation yourself, you could create a dangerous situation for other motorists and/or pedestrians.

A: The fuel gauge sending unit is attached to/on top of/inside the fuel tank. It might or might not be integrated into the fuel pump.

A: Your car should have a self-test/reset that you can run. Check your owner’s manual for specifics on how to do it.

A: Yes. Check your owner’s manual and the fuse box for its specific location.

Learn more with this video about diagnosing fuel gauge issues.

We’re here to be expert guides in everything How To related. Use us, compliment us, yell at us. Comment below, and let’s talk! You can also shout at us on Twitter or Instagram, here are our profiles. Got a question? Got a pro tip? Send us a note: guidesandgear@thedrive.com.

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