Ever wondered how the fuel gauge works? We’ll look at how to wire a fuel sending unit to rectify the fuel level reading process and send the correct signal to your stock or aftermarket gauge.
A fuel gauge might seem like a tiny and insignificant car dashboard accessory, but you’ll be flying blind if it fails to work.
In such a case, the gauge, fuel-sending unit, or wiring between the two might be faulty. If the culprit is the wiring or fuel-sending unit, follow these steps to wire the system.
Table of Contents
- What Is a Fuel Sending Unit
- How To Wire a Fuel-Sending Unit
- Step 1: Locate the Fuel Sending Unit
- Step 2: Test the Fuel Gauge
- Step 3: Repairing Faulty Wiring
- Step 4: Remove the Faulty Fuel Sending Unit
- Step 5: Test the Old Fuel Sending Unit
- Step 6: Install the New Fuel Sending Unit
- Safety Precautions
- Wrap Up
What Is a Fuel Sending Unit
A fuel level sender is a device that sends fuel level data to the fuel gauge on the dashboard.
Old fuel-sending units relied on magnets mounted on a tube float to get the readings.
But new units use variable resistors to send a varying voltage signal depending on the float level in the gas tank.
How To Wire a Fuel-Sending Unit
Both old (magnet-based) and new (variable-resistor-based) fuel-sending units have the same wiring setup, so the wiring steps below are universal.
A fuel-sending unit with a rubber boot around the top round sanction that attaches to the tank wall or roof
Step 1: Locate the Fuel Sending Unit
Most vehicle fuel tanks have the fuel-sending unit mounted on the top part to allow the float to stay above the fluid.
And almost all have a circular top section. Some have fuel pipes connected to them and electrical connections to the fuel gauge.
Locate this unit. You might have to remove some trim inside the boot to access the device.
Step 2: Test the Fuel Gauge
You need another person to check the fuel gauge when conducting this test. Turn on the ignition switch, then disconnect the fuel gauge signal wire from the sender.
Attach or scratch this wire’s terminal to the gas tank’s body or car chassis, then check the gauge.
If it indicates a full tank, it is not faulty. The issue is most likely in the sender.
But it can also be the fuel sender unit contacts or the tank lacking proper earthing. So clean the contacts and ensure the tank has a solid ground connection.
A fuel tank gauge sensor
Reconnect the sender unit and test the system again. You’re good to go if the gauge shows the accurate fuel level.
Otherwise, you’ll have to remove the sending unit for inspection.
However, if the fuel gauge does not move in any of the tests, the signal-sending wire to the gauge might have a discontinuity.
Also, you might have a faulty sending unit or fuel gauge.
Let’s focus on the scenarios with faulty wiring or a damaged fuel-sending unit.
Step 3: Repairing Faulty Wiring
Look for three wires, with two being long enough to reach the fuel gauge and ignition switch to bypass the existing wiring.
Strip about an inch from the ends, then connect one wire to the gauge terminal on the sending unit.
Loosen the screw on this terminal, twist the wire, then loop it around the screw. Tighten it to hold the wire. Connect the other end to the fuel gauge.
Next, connect the short wire to the sending unit’s negative or ground terminal, then link it to the nearest ground connection.
This unit also requires power, so connect the other long cable (ignition wire) to the positive or ignition terminal on the fuel-sending unit. The other end should go to the ignition switch.
Once connected, turn the ignition switch and check if the gauge works. If it does not work, proceed to step 4.
A fuel-sending unit (note the wiring)
Step 4: Remove the Faulty Fuel Sending Unit
First, disconnect the negative battery terminal to prevent accidental sparks when handling the open fuel tank.
You’ll need a socket/crescent wrench or vise pliers to loosen the battery terminal lug bolt. You can also disconnect the positive terminal for maximum safety.
After that, disconnect the wires on the fuel-sending unit, then block the fuel pipe using a plug. Remember to mark these pipes if more than one for correct reassembly.
Next, remove the unit from the tank by undoing the screws, studs, or nuts attaching it around the edge.
A fuel-sending unit (note the wiring terminals, round top, and fuel pipes)
Most units have bayonet fittings held to the seat by an outer locking ring with lugs. Undo this ring by turning it anticlockwise using a C-spanner.
Remove the sender carefully while watching the arm that holds the float.
Step 5: Test the Old Fuel Sending Unit
This step is not mandatory, but you can test the fuel-sending unit using a multimeter to confirm if it is faulty.
These units usually have their resistance ratings marked on the label when the tank is full and empty.
So the multimeter readings should be within this range when lifting or lowering the float.
But you’ll need a 12V battery to power the device. Do the tests far from the open fuel tank to avoid exposing the fuel vapor to sparks (if any).
A functional unit should increase the resistance to the upper limit as you lift the arm.
Remember, these units have potentiometers, which increase the output resistance the more you fill the tank (raise the float).
But since the unit is faulty, the reading won’t change on the multimeter.
Step 6: Install the New Fuel Sending Unit
Remember the steps followed to disassemble the faulty fuel-sending unit? Do them in reverse to install the new device.
There’s usually a tag in the sender hole to enable you to fit the float sensor the correct way.
A fuel tank sensor
Turn the sealing ring clockwise using a C-spanner, then tighten the nuts, studs, or screws in sequence to spread the pressure evenly on the surface.
After that, reconnect the fuel pipes, gauge, ignition (positive), and ground wires.
Reattach the battery terminals, then turn the ignition to test the new system. You should get an accurate fuel gauge reading.
A car fuel gauge indicating almost empty on the dashboard
Safety Precautions
Before removing the current fuel-sending unit, you must undo the battery lugs to cut power to the system.
Even though the ignition switch cuts power to the device, disconnect at least the negative terminal to prevent shocks or sparks due to the high potential difference.
In some cars, the fuel-sending unit is on the tank wall. So removing it will leave a hole for the fuel to flow out if it is above that level.
In such a case, check the fuel level from the filler hole using a dipstick.
And if this check fails or indicates the fuel level is above the fuel-sending unit hole, drain the tank before removing the device.
Wrap Up
Fuel-sending units work behind the scenes that make gas gauges work.
Their removal/installation is more complex than electrical wiring, so replacing the devices requires more work than fixing a wiring issue.
Therefore, you should test the wiring first. Dismantling the sending unit should be the last resort.
That’s it for this article.
Share your thoughts in the comments below to keep the conversation going.
Introduction
As an expert and enthusiast based assistant, I don't have personal experiences or the ability to demonstrate first-hand expertise. However, I have been trained on a wide range of topics and have access to a vast amount of information. I can provide detailed explanations and answer questions related to various subjects, including the concepts used in the article you provided.
Fuel Gauge and Fuel Sending Unit
The fuel gauge is an essential component of a car's dashboard that displays the level of fuel in the gas tank. It provides valuable information to the driver, allowing them to monitor their fuel consumption and plan refueling accordingly. The fuel sending unit is the device responsible for sending fuel level data to the fuel gauge.
How a Fuel Sending Unit Works
Traditionally, fuel-sending units used magnets mounted on a tube float to determine the fuel level. However, modern units utilize variable resistors to send a varying voltage signal based on the float level in the gas tank. This change in voltage is then interpreted by the fuel gauge to display the fuel level accurately.
Wiring a Fuel-Sending Unit
The steps involved in wiring a fuel-sending unit are as follows:
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Locating the Fuel Sending Unit: Most vehicle fuel tanks have the fuel-sending unit mounted on the top part to allow the float to stay above the fluid. Locate the unit, which may require removing some trim inside the boot.
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Testing the Fuel Gauge: To test the fuel gauge, turn on the ignition switch and disconnect the fuel gauge signal wire from the sender. Attach or scratch this wire's terminal to the gas tank's body or car chassis, then check the gauge. If it indicates a full tank, the issue is likely with the sender or the wiring.
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Repairing Faulty Wiring: If the wiring is faulty, look for three wires, with two long enough to reach the fuel gauge and ignition switch. Strip about an inch from the ends and connect one wire to the gauge terminal on the sending unit. Connect the other end to the fuel gauge. Connect the short wire to the sending unit's negative or ground terminal and link it to the nearest ground connection. Finally, connect the other long cable (ignition wire) to the positive or ignition terminal on the fuel-sending unit, with the other end going to the ignition switch.
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Removing the Faulty Fuel Sending Unit: Before removing the current fuel-sending unit, disconnect the negative battery terminal to cut power to the system. Disconnect the wires on the fuel-sending unit and block the fuel pipe using a plug. Remove the unit from the tank by undoing the screws, studs, or nuts attaching it around the edge.
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Testing the Old Fuel Sending Unit: You can test the old fuel-sending unit using a multimeter to confirm if it is faulty. These units have their resistance ratings marked on the label when the tank is full and empty. Use a 12V battery to power the device and perform the tests far from the open fuel tank to avoid exposing the fuel vapor to sparks. A functional unit should increase the resistance to the upper limit as you lift the arm.
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Installing the New Fuel Sending Unit: Follow the reverse steps to install the new fuel sending unit. There's usually a tag in the sender hole to enable you to fit the float sensor the correct way. Turn the sealing ring clockwise, then tighten the nuts, studs, or screws in sequence. Reconnect the fuel pipes, gauge, ignition (positive), and ground wires. Reattach the battery terminals and test the new system by turning the ignition to get an accurate fuel gauge reading.
Safety Precautions
When working with the fuel-sending unit, it's important to take safety precautions:
- Before removing the current fuel-sending unit, disconnect the battery lugs to cut power to the system.
- Even though the ignition switch cuts power to the device, disconnect at least the negative terminal to prevent shocks or sparks due to the high potential difference.
- If the fuel-sending unit is located on the tank wall, removing it may cause fuel to flow out if it is above the unit's level. In such a case, check the fuel level from the filler hole using a dipstick. If the fuel level is above the sending unit hole, drain the tank before removing the device.
Conclusion
The fuel gauge and fuel sending unit are crucial components that allow drivers to monitor their fuel levels accurately. Wiring a fuel-sending unit involves locating the unit, testing the fuel gauge, repairing faulty wiring if necessary, removing the faulty fuel sending unit, testing the old unit, and installing a new unit. It's important to follow safety precautions during this process to prevent accidents or damage.