Rajan Wilcox
A faulty fuel gauge can be a huge inconvenience, leaving you stranded on the side of the road. The most common cause of a faulty fuel gauge is a bad fuel level sending unit. This device measures the amount of fuel in your tank and sends a signal to the gauge. Other causes include faulty wiring, interrupted ground connections, corrosion, and loose connections. To fix this issue, you can either replace the sending unit or the entire fuel pump assembly. Alternatively, you can simply fill up your tank every few hundred miles or reset your trip meter each time you fill up to keep track of your mileage.
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What You'll Learn
Faulty fuel sending unit
A vehicle's fuel tank has a sending unit with a "float" that floats on top of the fuel supply, indicating fuel levels to the fuel gauge. The constant use of the sending unit means it is prone to wear and tear. If the contacts wear out, the circuits may remain open, and the fuel gauge may not change even when the fuel level does.
A faulty sending unit will result in an inaccurate fuel gauge. Symptoms of a faulty fuel sending unit include the fuel gauge getting stuck on empty or full, the fuel gauge behaving erratically, and the float breaking off or separating from the arm. A faulty resistor can also cause the gauge to read empty by restricting the signal.
You can test the sending unit with a multimeter. Place one probe on the sending terminal and the other on the ground. As you move the float, the resistance should change on your multimeter. If there is no change, your sending unit has likely failed.
If you have a sending unit with the fuel pump integrated into the assembly, you will have to replace the entire pump assembly when it fails. In some car models, you have to remove the fuel tank to reach the sending unit. A new fuel sending unit can cost anywhere between $25 to $800, depending on the brand, design, set inclusions, and intended vehicle.
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Damaged wiring
A malfunctioning fuel gauge can cause you to run out of fuel unexpectedly, potentially causing long-term damage to your vehicle. The fuel gauge system consists of the gauge, sender, and circuit. Issues can arise from any of these components, but most fuel gauge issues can be traced to a problem with the wiring near the tank or with the sending unit itself.
If your fuel gauge is malfunctioning, it is important to check the wiring for any damage. To do this, you should start at the gas tank and inspect the wiring harness. You should also check the ground connections, which can become corroded due to rain, snow, and salt. If you spot any corrosion, remove the connection, clean it, and then reattach it to the appropriate location. If you find a broken wire, you will need to replace it.
If your wiring and fuse test as passed, the next step is to remove the fuel sending unit/fuel pump assembly from the tank and inspect it. Sometimes, the arm or float will be broken, or the wiring leading up and out of the sending unit will be damaged. If you have an older vehicle with a 1-wire sending unit, resistance can be tested easily. Most older sending units are a "0-30" or "0-60" ohm sending unit, meaning that when the tank is empty, the resistance will read 0 ohms, and when full, it will read 30 or 60 ohms.
If your tests show that the ground is good and you have 12 volts at the gauge, take a jumper wire with alligator clips and connect the sender terminal to the ground terminal. If the gauge reads full, it is good. If not, it is bad and should be replaced. If your gauge is good, check the ground at the sender with your multimeter set to ohms. Look for a “no resistance” reading between the ground on the sender and your vehicle's battery ground. If your ground is bad, fix it. If the ground is good, use your jumper wire to short the sender positive terminal to the ground terminal. The gauge needle should read "full." If it does not, you will need to find and repair the break in your sender wire.
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Blown fuse
A blown fuse is one of the most common reasons a fuel gauge may not be working or is inaccurate. The fuel gauge is part of a complex system made of three main components: the gauge, the sender, and the circuit. These components work together to keep you informed of how much fuel is left in your tank.
The fuel gauge runs on electricity, requiring functioning wiring and circuitry. If there is a fault in the system, there might not be enough voltage for the gauge to read correctly. In some cases, the issue is because of an interrupted ground connection. However, any loose connection or corrosion can lead to issues.
If you have an older vehicle, the gauge should have two terminals. One is used to receive power any time the ignition is on, while the other is the wire coming from the sending unit. Test continuity between the sending terminal and the connection at the tank. If you don’t have continuity, you need to find a break in the wiring.
You can also test the fuel gauge by checking the resistance. With a newer vehicle, it can be nearly impossible to do this with the integrated instrument cluster. You might need to disassemble the entire cluster to get to the gauge, which is why it’s best to carefully inspect the wiring and sending unit first.
The least expensive fix would be to replace a blown fuse, which might only cost you $10, and you can easily do this yourself.
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Corrosion
One of the most common causes of fuel gauge issues is a faulty fuel level sending unit. This device measures the amount of fuel in the tank and sends a signal to the gauge to indicate the fuel level. Corrosion can impact the sending unit, causing it to malfunction or send inaccurate signals. The sending unit is usually located inside the fuel tank, where it can be exposed to fuel, moisture, and other contaminants that can lead to corrosion over time.
Additionally, corrosion can affect the wiring and electrical connections associated with the fuel gauge system. Corroded wires can interfere with the electrical flow, causing voltage and current degradation. This disruption in the electrical circuit can lead to inaccurate readings or even a complete failure of the fuel gauge. Corrosion in the wiring is typically caused by exposure to moisture, salt, or environmental pollutants. It is important to regularly inspect the wiring for any signs of corrosion, especially in areas prone to corrosion, such as the connections to the fuel pump module.
Furthermore, corrosion can also contribute to blown fuses, which are another potential cause of fuel gauge malfunctions. Fuses are designed to protect the electrical system, and when they blow, it can affect the fuel gauge's functionality. Corrosion, along with moisture and salt, can lead to blown fuses, requiring replacement to restore the proper functioning of the fuel gauge.
To address corrosion-related issues with the fuel gauge, it is important to identify the specific components affected by corrosion and take appropriate remedial actions. This may involve cleaning or replacing corroded parts, improving sealing or ventilation to reduce moisture exposure, or consulting a professional mechanic for more complex repairs.
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Instrument cluster failure
The fuel gauge is part of a complex system made up of three main components: the gauge, the sender, and the circuit. The sending unit is where the whole process begins. As your vehicle runs, the sending unit constantly monitors the level of fuel in the tank. However, this constant use means that it is prone to wear. If the contacts wear out, the circuits can remain open. In turn, the fuel gauge might think the voltage feedback means that the tank is either empty or full, depending on how the car is set up. In this case, the fuel gauge won't change regardless of how much fuel is in the tank.
The fuel gauge runs on electricity, requiring functioning wiring and circuitry. If there is a fault in the system, there might not be enough voltage for the gauge to read correctly. In some cases, the issue is due to an interrupted ground connection. However, any loose connection or corrosion can lead to issues.
To test the sending unit, set your multimeter to ohms. Place one probe on the sending terminal and the other on the ground. As you move the float, the resistance should change on your multimeter. If there is no change, your sending unit has failed. If you have a sending unit with the fuel pump integrated into the assembly, you will have to replace the entire pump assembly. In some car models, you have to remove the fuel tank to reach the sending unit, which makes the process more difficult.
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Frequently asked questions
The most common reason for this is a bad fuel level sending unit. This is a device that measures the amount of fuel in your tank and sends a signal to the gauge. It is usually located inside the fuel tank and can wear out over time or get damaged by dirt or corrosion.
Before you decide that you need a new fuel sending unit, make sure that the gauge fuse is not blown. Check your vehicle owner's manual or consult a mechanic to locate the fuse and check that it is working correctly. If the fuse is still good, then it is likely that part or all of your fuel sending unit is malfunctioning.
You can test the sending unit by setting your multimeter to ohms. Place one probe on the sending terminal and the other on the ground. As you move the float, the resistance should change on your multimeter. If there is no change, your sending unit has failed.
