Have you ever started your car knowing that your gas tank is reasonably filled, only to get jump-scared by that fuel gauge saying otherwise? You’re not alone, as many drivers – including yours, truly – have at some point experienced the same problem. If you’ve asked yourself: “Why is my car not registering fuel,” then we’ve got an answer for you.

There are a few possible culprits when it comes to failure to register fuel, but in most instances, it’s down to a faulty fuel level sending unit. Other possibilities include bad wiring between the sending unit and the gauge, then the gauge itself, and even a blown fuse.

Most solutions are fairly simple even though some might be relatively time-consuming. This article will shed some light on the possible problems and their fixes when it comes to a fuel gauge that’s not working.

What Does a Fuel Gauge System Consist of?

Before we move on to explaining different reasons behind a gas gauge malfunction, it’s important to get a grasp of the system’s innards and how they correlate with one another.

The entire system behind the fuel level reading consists of three parts:

• the fuel tank sending unit (fuel sender)
• the dashboard indicator unit (fuel gauge)
• the circuitry connecting them

If the fuel gauge on your dashboard is acting up, chances are the problem lies within one of these three parts.

How Does a Fuel Gauge System Work?

Here’s a rundown of a fuel gauge system’s operation.

Fuel sender

The fuel tank sending unit, which is typically accessible via the top of the gas tank (under the rear seat or in the boot), sends a modified voltage input to the gas gauge in the instrument cluster, which, in turn, displays the fuel level readout. Of course, there’s more to it than that since all parts within the fuel readout system consist of multiple sub-systems themselves.

The fuel sender consists of the fuel float connected to a potentiometer. The potentiometer itself is composed of a strip of resistive material attached to the ground via a small wiper. When the fuel level in the gas tank changes, the float moves within it, and the wiper follows suit across the resistor. The latter causes the change in voltage, which is indicated by the dashboard gauge unit as the fuel level we all know and understand.

Fuel sender inaccuracy

When the gas tank is full and the float is near the top, there’s very little resistance in the potentiometer, and higher amounts of current can pass through. You may have noticed that your car’s fuel gauge is inaccurate after topping the tank with fuel. This is because the float is submerged, and the wiper can’t move until the fuel levels drop. In other words, your car’s dashboard fuel gauge will inaccurately indicate a full tank of gas for some time.

Once the fuel levels start to drop, the float and wiper will move with it, the resistance will increase, and the reading will change. Similar to a full tank of gas, the readout will also be inaccurate once the levels drop low enough. The range of motion of the wiper doesn’t extend to the bottom of the gas tank, meaning the gauge will point out an empty tank even though there’s still some gas left.

Fuel gauge

The fuel gauge on the instrument cluster represents a visual readout of the voltage changes within the sending unit. They are either controlled by the instrument panel or the voltage input directly from the fuel tank sending unit.

Fuel gauge wiring

Of course, the fuel sender and the fuel gauge are connected via wires and circuitry. The fuel gauge wires also connect the two opposite ends of the system with the battery and ground.

Typical Problems With the Fuel Gauge System

Now that the fuel gauge system’s operation has been explained, let’s move to the typical problems most of us can encounter and give answers to the question: “why is my car not registering fuel?”

Faulty sending unit

A faulty fuel sender is the most common answer to the question: “why is my car not registering fuel?” Consisting of a few parts that are in constant motion, the fuel-sending unit tends to give out quicker and more often than other parts of the fuel system. With a faulty fuel sender, the fuel gauge will typically indicate either a completely full or empty tank of gas.

There are a few possible reasons for the fuel-sending unit to start acting up. A float might break off or otherwise get separated from the control arm. In such cases, the gauge should show an empty tank reading even when you fill the tank to the brim. A resistor can also go bad, and in such a case, the gauge might even show a full tank or move erratically across the dash.

Problems with wires

Although there are a lot of wires and circuitry between the fuel sender, the fuel gauge in the instrument panel, and the car’s battery, more often than not, it’s the wiring around the fuel sender that goes bad due to exposure to the elements. If your vehicle has a fuel sender that’s accessible by lifting the rear seat or trunk carpet – no matter how unconventional it sounds – its wiring might have even fallen victim to rodents.

Once the wiring gets loose or interrupted, the gauge will keep showing an empty tank and won’t budge until the connection is restored.

Faulty fuel gauge

Even a fuel gauge itself can fail, although that’s one of the unlikeliest of scenarios. The gauge has an internal circuit of its own that might fail in a specific area, such as between the full tank and half tank, for instance. Otherwise, it might fail completely and won’t show any reading until you fix it.

Faulty instrument cluster

A faulty instrument cluster is a slightly more common occurrence than a mere broken-down fuel gauge. Most modern cars use an integrated instrument cluster, meaning the circuits are intertwined, including the fuel gauge. Needless to say, if something fails in such a setup, there’s a high chance a few systems (including a fuel gauge) will fail as well. Fixing a modern instrument panel can be expensive compared to other problems related to fuel readouts.

Faulty fuse

Last but not least is a faulty or blown fuse. Considering it’s easy to determine whether the fuse is good or bad, checking the fuel gauge fuse is one of the first steps in identifying the problem. Most cars have a fuse box behind the dashboard. Identifying the right fuse shouldn’t be a problem with a fuse map in the owner’s manual. However, many cars don’t necessarily have a separate fuel gauge fuse, but one that’s integrated with the instrument cluster.

Final Words

If you wonder why your car is not registering fuel, the reasons are usually pretty straightforward. It all comes down to either the faulty fuel tank sending unit, a broken-down fuel gauge on the instrument cluster, or interrupted wiring, including the fuses. Solutions to most of these problems are relatively simple and inexpensive, except for a broken-down instrument cluster that might be a rather expensive repair depending on the car model. Regardless of the price tag, it’s imperative to get the fuel gauge problem fixed sooner rather than later, as being left stranded without gas isn’t only distressing, but potentially a lot more expensive than what fixing the issue would have been in the first place.

FAQ

How much does it cost to fix a fuel sender?

Depending on the type of car you own, fixing a fuel tank sending unit (parts and labor included) could set you back between $250 for conventional cars and $800 for more luxurious models. The breakdown of parts and labor costs also depends on the car model but typically swings in favor of labor costs.

How much does it cost to fix an instrument cluster?

Fixing an instrument cluster costs between $800 and $1,000 on average, but more expensive vehicles tend to incur repair costs even higher than that.

How much does it cost to replace a fuse?

Replacing a fuse is one of the cheapest jobs you can do on a car and also one that you can easily do yourself. The fuse typically costs between $10 and $20, but some models utilize fuses that can cost $100 or more.

Is a fuel gauge easy to fix?

It depends on the problem behind its malfunction. If it’s a blown fuse, it’s fairly easy to identify and fix the problem. Even separated wiring can be easy to fix provided there’s easy access to it. However, fixing a faulty fuel sender or a broken-down instrument panel can be time-consuming and should probably be left to a professional.