Fuel gauge - the only guide you need

Running out of gas in the middle of the road can be exasperating or even running late for a meeting and realizing that you are out of fuel, can as well ruin your mood. Many people are used to understanding how a fuel gauge works; they know when their fuel tank is full or empty.

But what happens when your car’s fuel gauge is not working and you cannot figure out how to check your car’s fuel level? A gauge is one of the most essential parts of a vehicle, so knowing and understanding a gauge is important.

What is a fuel gauge?

fuel gauge

A fuel gauge is a measuring instrument that is used to help determine the amount of fuel in an automobile or vehicle.  A gauge is made up of two parts, which are, the indicator and a sending unit. The indicator is the part of the gauge that is located on the dashboard of the car, while the sending unit is located in the fuel tank.

Types of fuel gauges

There are 3 types of fuel gauges that have ever been made up until today. They are Analogue resistance, Analogue magnetic, and electronic fuel gauges.

Analog resistance fuel gauges

Analog resistance fuel gauge

These types of fuel gauges were used in the early 1980s. They used a bimetal strip to move the indicator needle around the gauge. The bimetal strip gets heated when the current passing through the gauge heats up. Once the bimetal strip is heated up, the strip then expands. This helps to determine how far the indicator needle moves on the fuel gauge.

The amount of current that flows through the gauge is maintained by the ground circuit from the sending unit located in the fuel tank. Voltage is supplied by a voltage regulator in the instrument panel, which helps to reduce the circuit voltage to five volts. This voltage regulator also helps to supply the temperature and oil pressure gauges.

Analog magnetic fuel gauges

Analog magnetic fuel gauges

These types of fuel gauges were introduced in the late '80s as a replacement for the analog resistance gauge. The magnetic fuel gauges have a small magnet on the indicator needle.

The tank unit has a variable resistor, that its resistance floats from up to down. The floating is created by three coils, and when the car's ignition is switched on, current flows from the coils. The current then produces magnetic fields that control the fuel indicator needle in the gauge.

When the fuel level in the car is high, the resistance in the fuel sending unit is also high, and this magnetic force pulls the indicator needle to the right. But, as the fuel in the car reduces, the resistance in the sending unit reduces. The magnetic force also reduces and this pulls the indicator needle to the left to show that the fuel tank is almost empty and needs refueling.

The magnetic gauge is faster in reading the fuel level in a car, compared to the analog resistance gauge which can take up to two minutes to read.

Electronic fuel gauges

Electronic fuel gauge

This type of gauge was also introduced in the 80s and it is still in use up till today. The electronic fuel gauge uses vacuum fluorescent or Liquid Crystal Display (LCD) to indicate the fuel level on the fuel gauge. Many electronic fuel gauges display E, ½, F, and it operates in the same way as the other two types of fuel gauges.

But distinctly. In that, the sending unit can produce results based on the variable resistance ground path. The electronic gauge also displays vital information like fuel remaining, trip distance, average fuel economy, and more.

An electronic gauge also can show alerts to the car driver that the gauge system is faulty and needs fixing. Now that you understand the types of fuel gauges that there are, it’s time to also learn more about the most important component in a gauge system.

Without this component, it is almost impossible to get a correct reading in the fuel gauge. This component determines what reflects on the fuel gauge and what the fuel indicator shows.

The fuel gauge sender

The fuel gauge sender

The fuel gauge sender is found in the fuel tank of a car. It is attached to a metal rod that measures the electrical flow of the car and also the fuel in the car. Once the fuel sender is not working, the fuel indicator will read wrongly.

How does the fuel gauge sender work?

Fuel gauge mechanism

This component also called the fuel sending unit is made of a float, which consists of foam attached to a very thin metal rod. The end of the metal rod is attached to a variable resistor that changes according to the position of the float.

The resistor is designed to resist the flow of electricity, so the more the resistance, the less the current that flows. The float is made to float on the surface of the fuel inside the car's fuel tank. As the level of the fuel in the tank reduces the position of the float changes and in turn, moves the resistor which controls the display on the fuel gauge.

When the fuel gauge sender has an issue, it affects the fuel gauge, which in turn causes a car to run out of fuel without the driver knowing. But, with an electric fuel gauge, the driver can be alerted when the fuel sender has gone bad and is affecting the gauge.

Symptoms of a faulty fuel gauge sender

Symptoms of a faulty fuel gauge

A faulty fuel gauge sender in turn affects the fuel gauge. So, how do you know when the gauge sender in your fuel tank has developed a fault?

When the fuel indicator needle is stuck on empty

The gauge keeps reading empty even after refueling the car, your fuel sender is faulty. If the float of the sender becomes separated from the arm, which is the metal rod, it can cause the fuel level to stay empty. Also, a faulty resistor can cause the fuel gauge to be stuck on empty.

When the indicator is stuck on full

Also, when the fuel sender becomes faulty, it also causes the fuel gauge to read empty. A faulty resistor can cause this likewise.

When the fuel gauge is inconsistent

This means the faulty fuel gauge sender can cause the indicator to change positions wrongly. You may have your fuel tank filled up, but when the faulty sender has not been fixed the fuel gauge will cause the indicator to read between full and empty as it likes.

Fuel pressure gauge

Fuel pressure gauge

The fuel pressure indicator helps to show you the pressure of the fuel entering the carburetor. The fuel pressure gauge is a part of the vehicle's fuel system that is responsible for regulating the pressure of the fuel flowing through the fuel system. Different types of car engines all require varying amounts of fuel and this amount can be metered by changing the fuel pressure.

Some developed cars have their own in-built electronic fuel pressure gauge or regulator. While some other types of cars require an external fuel pressure gauge. The fuel pressure gauge shows the pressure of the fuel in the tank. While the fuel pressure regulator helps to distribute fuel to the engine of the car. Any fault in the fuel gauge regulator poses a problem to the vehicle.

Apart from ensuring the right mixture of air and fuel in the vehicle, this component has other importance. You can find out in this article written on the fuel pressure regulator.

The fuel pressure of a car is crucial for optimal performance and longevity of a car. So, if the fuel pressure of your car is too high or too low, how do you know?

The correct fuel pressure helps a car to run smoothly without any fault so that the power and fuel economy of a car is best optimized. If the fuel pressure in your car is too high, it means that your car has been over-fueled, and this can lead to many symptoms which in turn lead to damages.

Also, if the fuel pressure in a car is too low, your vehicle will lose its horsepower and the engine would stall.

Symptoms of high fuel pressure

  • Constant refueling of the car or low fuel economy.
  • Poor car engine performance
  • The exhaust produces a fuel smell
  • The spark plugs have been blackened
  • The spark plugs have become wet with fuel

Symptoms of low fuel pressure

  • Low acceleration
  • Unresponsive throttle
  • Stalling engine
  • Misfires
  • Clogged fuel filter

How do fuel gauges work?

Fuel gauge

Fuel gauges have two markings, F for full and E for Empty. So, for a gauge to be reading or working properly, it has to read between the two markings. Some cars have ½ to show that a fuel tank is at half, but this marking is not common. The important thing to a car driver should be to know when a car is full and when it is becoming empty.

The gauge needs to measure the voltage across the resistor. But the resistor also has to show the amount of fuel in the car’s fuel tank. For a car to be able to read its fuel level properly, the fuel sender has to be working properly without fault. Since the sender moves vertically with the changing fuel level. As the car is in transit, the opposite end of the level moves across the resistor.

Which in turn causes a change in the voltage supply to the gauge. The change in the voltage supply causes the fuel indicator needle to show the accurate fuel reading on the gauge.

More on fuel gauge functionality

The fuel sender and the resistor work hand in hand to ensure that the accurate fuel reading is displayed on the fuel gauge. Although, for an electronic gauge the sender relays with an electronic circuit. The electronic circuit from the sender triggers a warning light when the fuel level in the tank is too low. The warning signal varies from one automotive brand to another.

But when the warning signal starts, usually the fuel remaining can only travel 30km to 60km.Some recently developed cars using the electronic type of gauge with the LCD have updated display methods on the dashboard. An electronic processor receives the signal from the fuel sender and converts these signals to digital signals, which are displayed on the dashboard.

Reasons why your gauge is not working

The primary reason why your indicator is not working is that the fuel sender or fuel sending unit is faulty. There are other attributed reasons, but a faulty fuel sender is the main reason. So, if you notice that your gauge is messing up and cannot seem to read the fuel level properly, these listed reasons are why.

A faulty fuel sending unit

This reason is a primary one, as the fuel sender may have broken in the fuel tank or the parts may have become disjointed. The indicator will read the voltage information and show the fuel level as full, empty or the needle will become erratic.

When a car is in use constantly, the fuel sending unit is also in use, moving against the resistor. The frequent movement against the resistor can result in wear and tear causing the sender to become faulty.

Circuit problems

A voltage may be absent in the fuel sending unit and the gauge will be unable to receive any motions from the voltage, as per normal. The constant movement of the sender against the resistor brings about voltage. And it is the voltage that sends the message to the gauge. Once there is a problem within these circuits, no voltage is produced, therefore causing the gauge to read wrongly.

Gas gauge failure

The internal circuit consisting of the sender, the resistor, and the produced voltage may become faulty. Any one of these components may be open, thereby causing a short circuit. A short circuit will be unable to pass any information to the gauge.

A faulty instrument cluster

Instrument clusters are made of fully integrated circuits and they sometimes have replaceable bulbs. If a bulb is bad, it, in turn, affects the gauge. If a gauge becomes bad from a faulty instrument cluster, then the whole unit has to be replaced. This reason is the most expensive reason to fix in a gauge.

Ways to fix a faulty gas gauge

Fix a faulty gas gauge

Fixing a faulty indicator depends on why the gauge is not working in the first place. Also, the amount of money you spend depends on the reason behind the faulty gauge. To run a diagnostics on your car to know the exact problem, check if your car was made in the last 20 years. If yes, then you have to check the owner's manual for the instrument clusters self–test procedure.

This involves holding the odometer down, as you start the car's engine. This method helps to test the instrument's panel gauges and lights. During this method, the gauge should fluctuate between full and empty. If the indicator does not move at all, it shows that the gauge is faulty.


To fix a faulty fuel meter, it is best to take your car to an auto-workshop to get a professional to work on your car. This works better than fixing it for yourself and ending up with more complicated issues.A fuel sender is the most important part of a gauge and once it becomes faulty, the gauge develops a fault as well. Being another gauge important to vehicles, check out this article on the vacuum gauge.

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