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HomeTips & GuidesWiring Fuel Sending Unit – Detailed Replacement and Wiring Steps

Wiring Fuel Sending Unit – Detailed Replacement and Wiring Steps

Wiring Fuel Sending Unit: It’s inconvenient to drive your car without knowing your correct fuel level. To avoid this, I recommend ensuring you don’t have a faulty fuel-sending unit that measures your fuel level. 

Here, I will show you steps for wiring the fuel-sending unit, ensuring your fuel gauge reads your fuel levels correctly. 

But before that, let’s first see what a fuel-sending unit is, its types, and the symptoms of a faulty one.

What is the Fuel Sending Unit (Fuel Level Sensor)

Also known as the fuel level sensor, the fuel-sending unit measures the amount of fuel in your car fuel tank. 

It then sends this information to the dashboard fuel gauge, showing you how much fuel you have. 

Your fuel level sensor typically features a buoyant floating mechanism that goes up and down your fuel tank. 

To measure fuel level, you connect this float to a variable resistor that changes resistance depending on the float’s position. 

For instance, when your tank is full, the floater is at the top, and the variable resistor resistance is low.

On the other hand, the variable resistor resistance is highest when the floater is at your fuel tank’s bottom.

 This variation in resistance generates electrical signals sent via a harness to the fuel gauge on your dashboard. 

Your fuel gauge then interprets this electrical signal, showing your tank’s fuel position on the display using a pointer.

Fuel sender gauge for a car

Fuel sender gauge for a car

Types of Fuel Sending Units

As you may expect, there are many types of fuel level sensors that you can use to measure your fuel level.

 Here, I will talk about the common 4 together with their working mechanism, pros, and cons.

Resistive/Floating Fuel Sensor

Resistive fuel sensors are the most common ones installed in your vehicle from the factory. It uses a float and a variable resistor, as explained above. 

Most people love this device because it’s easy to install, cost-effective, and has no maintenance.

 Despite this, its accuracy levels are low, especially when negotiating corners and cruising at high speeds. 

Additionally, the oil tank shape limits its installation position, bringing accuracy issues. 

The last disadvantage is that the sensor is prone to wear and tear due to sliding, reducing its lifespan.

Capacitive Fuel Sensor

A capacitive fuel sensor measures your fuel level using the ability of a system to store charges (capacitance). 

It features two plates separated by an insulator; one plate is fixed while the other moves with the oil level. 

The capacitance changes as your fuel fills or empties the space between the two plates. This capacitance reading generates electrical signals sent to your fuel gauge.

 The gauge interprets this as fuel level and displays it on your dashboard gauge. 

You may like this sensor because it’s durable, accurate, and resistant to turbulence and wear and tear. 

However, its installation demand and humidity and temperature affect its accuracy.

Ultrasonic Fuel Sensor

Ultrasonic fuel level sensors are noncontact devices that use ultrasonic sound waves. You have a transducer that emits an ultrasonic pulse and sends it to your fuel surface. 

Then, the fuel surface reflects this pulse, and the same device receives it as sound waves.

 It then calculates the distance between the liquid level and the sound receiver based on the time to send and receive the sound signal. 

What I love about this gadget is that it’s easy to install, with high accuracy, stability, and no maintenance. 

All in all, factors like dust, temperature, and humidity may affect its readings’ accuracy.

A car fuel gauge reading

A car fuel gauge reading

Pressure sensor

Here, you have the most used pressure sensor, the hydrostatic type. Place it at the tank’s bottom and measure the fuel pressure. 

The sensor can determine the fuel in your tank based on the tank’s volume and the weight of the fuel above it. 

Press sensors are cost-effective and easy to install; vapor and other external factors don’t affect them. 

On the negative side, they may provide inaccurate readings if your fuel density isn’t uniform.

Symptoms of Faulty Fuel Sending Unit

One of the most obvious symptoms to expect is your fuel gauge giving you inaccurate readings every time. 

While this can also mean a faulty gauge wiring harness, the biggest culprit is the sensing unit due to its location.

 Other symptoms may include your fuel gauge being stuck on empty even if you know you have fuel in your car. 

While here, note that the gauge may stay full even when your fuel tank is empty. 

Your fuel gauge might also move abnormally or fluctuate when the sending unit is faulty. 

Note that when all is well, the gauge pointer moves slowly toward the empty without moving up and down.

How to Check Fuel Sending Unit

Before checking the fuel-sending unit, you must know its location on the tank’s top or side.

 Now inspect if your unit is well on the tank and also inspect any corrosion or physical damage. 

You may clean its connectors for dirt and corrosion to facilitate connectivity and ensure firm grounding. 

From there, test if it’s receiving the correct voltage by backprobing its connectors while the battery is on. 

You may check its normal voltage from the manual; if the testing result shows otherwise, it’s faulty.

Checking the Sending Units Resistant

You must remove the device from the fuel tank and test it for resistivity at different levels. You should check its manual to know how to remove it and the resistivity to expect. 

When it’s down, now place one probe of the multimeter to the voltage pin at the top of the device. 

Then, play with the float arm, move it at different areas, and test the Ohm you get on the multimeter. 

From our discussion above, you can expect the Ohm to increase when the float arm moves downwards. 

If the resistance fluctuation is correct then your device wiring has an issue. 

On the other hand, if the Ohm reading is not fluctuating, you will need to replace the whole device. 

Note that this device can serve you a lifetime but issues with your fuel may limit its longevity.

Using a multimeter gauge on a car hood

Using a multimeter gauge on a car hood

How to Replace Fuel Sending Unit

  • First, youmusto release your fuel tank pressure based on the instruction manual advice.
  • Then, unplug the sending line and other electrical connections from your sending unit and remove the retainer ring.
  • From there, wipe clean the area around the plug to ensure no contaminants in your fuel tank,
  • You may then remove your existing fuel-sending unit and make sure it resembles the new one
  • Now, use a new gasket to install the new device and align it properly
  • For the fuel pump, make sure you guide the unit arms first to their position
  • You may now return the retainer ring to its position and secure it with screws and washers
  • Finally, connect all the electrical connections you moved and the fuel lines.
  • Then, test your device to see if it functions
Checking a fuel level sensor

Checking a fuel level sensor

How to Wire Fuel Sending Unit

Here, I will tell you how to wire the ultrasonic fuel sensor, but you need the following tool:


  • A corner drill, bi-metal hole saw, metal drills, flathead screwdrivers, pliers, a riveter, and a hacksaw are also needed.
  • You also need a laptop, USB cable, U-bolts, and another technician to help you. Note that this installation requires knowledge and expertise in fuel tank and level sensors.

Ultrasonic Fuel Sensor Installation

  • Before any installation, polish your fuel tank‘s bottom, where you will glue your sensor.
  • Now, find the central bottom point of your fuel tank where the sensor will go.
  • Then apply the included glue on your sensor and place it at the bottom of the fuel tank.
  • From there, press it to install it in the center and use the tank’s metal bands to fasten it snuggly.
  • When through, connect it to the dashboard and your laptop using its special cable and then download its software.
  • Then, use the software to calibrate your fuel tank. 
  • Lastly, disconnect your sensor from your laptop and link it to the tracker.


While I believe my research can help you install your fuel level sensor, I recommend seeking a technician for professional installation.

I am Lillian Yang, having been a sales manager for over 10 years.

I have received many positive reviews from customers. They have praised our excellent service, on-time delivery, and high-quality cable assemblies.

For your projects, please provide cable assembly files/images/smples, etc., so that I can send you a quotation within 24 hours.

Contact me now and let’s get started on building your wire harnesses!

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