What Is Fuel Gauge And How To fix a Bad Fuel Gauge?

What is Fuel Gauge?

In automotive and aerospace engineering, a fuel gauge is an instrument used to indicate the amount of fuel in a fuel tank. In electrical engineering, the term is used for ICs determining the current State of Charge of accumulators.

How does a fuel Gauge work?

The fuel sending unit is located in the gas tank to measure the fuel tank level. Some sending units are attached to the fuel pump assembly, while others are stand-alone units, but both are made up of the same three components: float, a metal rod/arm, and a variable resistor. These three components work together to measure the vehicle’s fuel level and relay the information to the gas gauge.

  • Float: The float, which is made of a buoyant composite or foam, floats on top of the fuel in the tank.
  • Metal rod or arm: The float is connected by a thin metal rod to a contact inside the variable resistor.
  • Variable resistor: A resistor is an electrical device that resists the flow of electricity, and a variable resistor has the ability to adjust the amount of resistance voltage encounters by sliding a contact (wiper) over a resistive element. The wiper is connected to the fuel gauge either directly by wire, or indirectly to an electronic device that communicates with the fuel gauge. In a fuel sending unit, the variable resistor receives power via a small coil from the vehicle’s battery, which is used as the baseline signal.

The fuel sending unit is one of many terms associated with this auto part. Luckily, these names are interchangeable because they all refer to the same part with the function of measuring a vehicle’s fuel level.

Fuel Gauge

How a fuel sending unit measures fuel tank levels

The float in the fuel tank will move up or down according to the fuel level. The metal rod pivots in relation to the float, which causes the wiper inside the variable resistor to move as well. The wiper moves along a strip of resistive material connected to a ground on one end, and the strength of the electric current from the resistor is determined by the position of the wiper to the ground.

The wiper sends the electric current to the fuel gauge, which displays the fuel level accordingly on the vehicle dashboard.

Fuel sending units work differently depending on the manufacturer. For example, a Ford fuel sending unit will be further from the ground on a full tank, while a GM fuel sending unit of the same year will be closest to the ground on a full tank. To understand how your vehicle’s fuel sending unit reads resistance, consult the service manual.

When the fuel tank is completely full, the wiper is either closest or furthest from the ground on the resistive material strip. Here is where there is either the least amount of resistance or full resistance respectively.

When a vehicle is almost out of fuel, the wiper again is either closest or furthest from the ground as float rests at the bottom of the metal rods travel. Depending on its specifications, the fuel gauge will show full or empty according to what resistance it reads as full or empty.

As the fuel level along with the float lower in the tank, the metal rod connected to the float either moves the wiper further or closer to the ground, which either restricts or increases the amount of electric current being sent to the fuel gauge. The fuel gauge display drops from full according to the resistance change.

What Causes the Fuel Gauge Not To Work?

The fuel gauge can act up as a result of 5 components of the fuel gauge system that may be broken and need maintenance or replacement. An inaccurate fuel tank reading is most commonly caused by the sending system which reads the fuel tank level and sends the reading to the gauge.

Issues can also stem from a bad gauge, blown fuses, or corroded wiring. You can self-test all of these parts at home with a few tools. If you’re interested in doing this, check out the detailed step-by-step guide at the end of this article.

1. Is There a Fuse for The Gas Gauge?

Yes, there is a fuse for the gas gauge. Every component of your vehicle that uses electricity will have some form of connection with the fuse boxes in your car. That’s right, a car will typically have more than one fuse box! Traditionally one will be located under the steering column on the inside of your car on the driver’s side. There is also a fuse box located under the hood for most vehicles.

For accurate information regarding what fuses are in what fuse boxes as well as where to find these fuse boxes refer to the owner’s manual of your vehicle. Blown fuses can definitely be a cause of a gas gauge not reading properly and can be worth looking into as it is one of the easiest and cheapest repairs to make regarding this problem.

2. Signs That You Have a Bad Fuel Gauge

The signs of a bad fuel gauge are pretty straightforward. If your fuel sensor needle moves erratically or more quickly than you feel you are burning fuel this is likely indicative of an issue in your fuel gauge system.

Alternatively, the gauge may read F and E all the time regardless of how much fuel you actually have. In some cases, the fuel gauge will randomly read E and this can be fixed simply by turning your car on and then back on. This is likely caused by a wiring or sending unit issue.

3. Can You Drive with A Bad Fuel Level Sensor?

Yes, you can absolutely drive your car with a bad gas gauge though it can be a bit like playing with a chance if you are not diligent in filling up your car regularly. Generally fixing your fuel level sensor is fast and inexpensive to repair, but if you’re in a tight spot and can’t repair this item really the worst that is going to happen is that you run out of gas. Which can of course lead to more problems.

How To Fix the Gas Gauge on My Car?

A stuck fuel gauge on your car is not only annoying, it is also a hassle as you need to keep track of the number of miles you have driven since your last fill-up to prevent you from running out of fuel.

A fuel gauge functions using a series of electrical connections from the sending unit to the gauge cluster, and when one of these connections fails, so does your fuel gauge. The good news is, you can troubleshoot the problem yourself and avoid an expensive repair. Here’s how you can do it:

Step 1: Turn the ignition on and off a few times, and observe if the needle on the fuel gauge moves. If the needle does not move, it most likely means you have a blown fuse and it is due for replacement. The fuse box can either be found on the driver’s side dash or in the engine compartment. Refer to your car owner’s manual to find out where your fuse box is located.

Step 2: Test the grounding wire on the sending unit of the fuel tank. This is connected to your car’s fuel tank. You can do this by attaching the negative jumper cable to the vehicle’s frame, and the positive jumper cable to the sending unit’s grounding terminal. When the fuel gauge is working when the jumper cables are connected, it means you need to replace the grounding wire on the sending unit.

Step 3: Disconnect the wiring connected to the sending unit of the fuel gauge and then look at the fuel gauge. If the fuel gauge is now showing an empty reading, it means the fuel gauge is faulty and needs to be replaced. On the other hand, if your fuel gauge is showing a full reading, it means the sending unit is faulty and due for replacement.

Step 4: Check to confirm that all of the wirings is securely connected to the back of the fuel gauge. To do this, you have to remove the dashboard to have access to the instrument cluster. Consult your car owner’s manual as the process to do this varies from vehicle to vehicle. 

Also, check the fuel gauge’s grounding wire by connecting the negative jumper cable to the car’s frame and the positive cable to the grounding terminal of the fuel gauge. Turn the ignition on and check the fuel gauge if it is working or not. If it is working, then the grounding wire should be replaced.

How Much Does It Cost to Fix A Fuel Gauge?

The cost is going to vary depending on what the issue is. An issue can be resolved with a new fuse costing $10 or a fuel gauge sender replacement can cost up to $800 after labor. The answer is it depends. Here is a breakdown of the common parts that would need replacing and their cost.

Cost Of Replacing the Fuel Gauge Sender

The majority of the time it is the fuel gauge sender which is the problem. This part can be a bit pricey to repair and most of the expense is in labor costs. Depending on the make and model of your car and the specific sender that you purchase, costs will run on average between $250 and $800. You can save a lot of money replacing this part yourself if you feel comfortable.

Cost Of Replacing the Fuel Gauge Fuse

Another replacement part that may fix your fuel gauge is the fuse. This is very inexpensive and easy to do yourself. On average the cost of replacing a fuse is between $10 and $20 but some specialty fuses will cost around $100.

Cost Of Replacing the Fuel Gauge

If it is the gauge itself that is your issue, you’re in luck. This part is pretty cheap to replace and depending on the make and model of your car will cost between $50 and $200 for the part. You will have to consider the labor of replacement if you intend on having this replaced professionally. Total costs will be between $200 and $400.