Bad Fuel Sending Unit Symptoms, Causes, and How To Replace It

The fuel gauge sender, often called the fuel sending unit, is a crucial component of your vehicle located in the fuel tank. The primary function of the fuel gauge sending unit is to send the necessary signals to operate the fuel level gauge in the instrument cluster. If the fuel sending unit encounters any problems, it may adversely affect the accuracy of the fuel gauge, potentially leading to fuel-related problems and the risk of consumption of higher fuel than usual. This article explains the bad fuel sending unit symptoms, causes and how to test it. 

What is the Function of a Fuel Gauge Sender?

The fuel gauge sender, known by various names such as the fuel level sending unit, fuel sending unit, or float gauge, plays a crucial role in transmitting fuel tank level information to the fuel gauge. Composed of three key components, it ensures accurate fuel level readings.

Fuel Gauge Sender

It has a buoyant float constructed from materials that resist fuel corrosion. This float is attached to a metal rod, which in turn links to a variable resistor. As the fuel level changes within the tank, the float adjusts its position accordingly. Consequently, the metal rod moves alongside the float, providing input to the variable resistor.

Positioned atop the fuel, the float and rod arrangement collaborate to reflect the quantity of fuel present.

By measuring the position of the rod, the variable resistor determines the fuel level and transmits this information as an electrical signal to the car’s system. The fuel gauge in the instrument cluster then interprets this signal and presents the corresponding fuel level to the driver, ensuring they are aware of when it is necessary to refuel.

Symptoms of a Bad Fuel Sending Unit

When the fuel sending unit goes bad, it produces one or more of the below-given symptoms:

1) Fuel Gauge is Stuck on Empty

The float in the fuel sending unit can occasionally become detached from the arm, leading to potential issues. Additionally, there may be something wrong with the variable resistor.

Fuel Gauge is Stuck on Empty

In certain cases, the fuel sending unit may cease to transmit current at specific positions, resulting in an empty reading. This typically occurs when the resistor either generates maximum resistance or prevents current flow.

2) Check Engine Light

Under certain conditions, a bad fuel sending unit can trigger the illumination of the check engine light on your vehicle’s dashboard.

Check engine light

When the engine control unit (ECU) of your vehicle detects wrong fuel level measurements and reads them as a potential fuel system problem, it may activate the check engine light as a precautionary measure. Therefore, the check engine light coming on could be a consequence of an anomalous fuel sending unit.

Read More: How To Reset Check Engine Light

3) Erratic Fuel Gauge

Ideally, the fuel gauge of your vehicle should always display a smooth and consistent progression towards empty as fuel is consumed.

If the fuel gauge exhibits erratic behavior or unusual fluctuations, it is one of the clear symptoms of a bad fuel sending unit. To verify the functionality of the fuel sending unit, you would require a multimeter and access to the fuel tank.

4) Incorrect Fuel Gauge Readings

Faulty readings from the fuel gauge are not limited to being stuck at full or empty; they can occur at any position due to a malfunction. While it is uncommon for the gauge to get stuck at an uneven place, it is not impossible.

However, it is important to consider that this issue can also be attributed to a defective fuel gauge, necessitating a comprehensive diagnosis before reaching conclusions.

5) Fuel Gauge is Stuck on Full

Fuel Gauge is Stuck on Full

When a fuel gauge remains stuck on full, it commonly indicates a faulty variable resistor. A bad resistor provides inaccurate information to the fuel gauge, forcing it to consistently display a full reading. However, a faulty fuel sending unit may also lead to this issue.

Causes of a Bad Fuel Sending Unit

The fuel sending unit goes bad due to one or more of the below-given causes:

1) Faulty Fuel Level Sensor

The fuel level sensor in the fuel sending unit consists of a float attached to a variable resistor. Over time, the fuel level sensor can be damaged, resulting in inaccurate readings or complete failure. This can be caused by different factors such as electrical, corrosion, or mechanical wear issues.

2) Wiring Issues

Damage to the electrical wires connecting the fuel gauge to the fuel sending unit and the vehicle’s electrical system is another potential source of problems. Short circuits, frayed wires, or poor wiring connections can disrupt the message between the gauge and the fuel sending unit, leading to incorrect fuel level readings.  

3) Age and Wear

Over time, the fuel sending unit may experience gradual deterioration due to regular wear and tear, similar to any other mechanical part.

Continual exposure to fuel, vibrations, and temperature fluctuations may progressively degrade the parts of the fuel sending unit, undermining its reliability and accuracy.

4) Physical Damage

Due to its location inside the fuel tank, the fuel sending unit is susceptible to physical damage caused by corrosion, collisions, and external factors.

Unintentional impacts, rust, or severe environmental can compromise the integrity of the fuel gauge sending unit, leading to wrong fuel level readings.

5) Dirty Fuel

Regular exposure to dirty fuel may also lead to the failure of the fuel gauge sending unit in a vehicle. Water, dirt, or sediments in the fuel may accumulate around the fuel unit, impacting its performance and eventually causing a failure.

How to Prevent a Fuel Sending Unit from Damage

1) Use Good Quality Fuel

To prevent the buildup of contaminants that can affect the fuel sending unit performance, it is advisable to use good-quality fuel. Refrain from refueling at fuel stations known for low-quality fuel and always choose trusted fuel stations for refueling.

2) Proper Maintenance

Ensure a regular maintenance routine for your car’s fuel system. This includes periodic inspections of the fuel sending unit, fuel filter replacements, and fuel system cleanings.

Adhering to the manufacturer’s recommended maintenance intervals helps keep the fuel system in optimal condition and reduces the likelihood of fuel sending unit issues.

3) Avoid Overfilling the Tank

Don’t overfill your fuel tank, as it may lead to fuel leakage and potential damage to the fuel sending unit. When refueling, exercise caution and don’t fill your tank when the fuel nozzle clicks off, indicating that the tank is full.

4) Proper Fuel Handling

Proper handling of fuel is crucial to prevent impurities. Don’t introduce foreign objects, such as water or dirt, into the fuel tank, as these may damage your fuel sending unit and other components of the fuel system. You should always use clean and approved containers for fuel storage.

5) Fix Electrical Issues

Electrical issues, such as loose connections, may contribute to malfunctions in the fuel sending unit. To prevent further damage, it is essential to promptly address any deviations in the fuel gauge or other electrical problems by seeking assistance from a professional mechanic.

6) Monitor Fuel Consumption and Performance

Stay attentive to your vehicle’s fuel level and performance. Be alert for any sudden changes, such as a significant drop in fuel efficiency or unpredictable readings on the fuel gauge. If you notice any unusual patterns, it is advisable to have your vehicle inspected by a mechanic who can find and resolve the possible issues of the fuel sending unit.

Implementing these preventive actions can help reduce the likelihood of encountering problems with the fuel sending unit and contribute to its proper functioning. Proper fuel handling, regular maintenance, and timely repairs are key factors in ensuring the longevity and efficiency of the fuel system.

How Do You Test a Fuel Gauge Sender?

Follow the below-given steps to test a fuel sender unit:

1) Scan Trouble Codes

If the check engine light is flashing, you can gain insights into the underlying issue by retrieving data through the OBD2 scan tool.

To do so, connect a scan tool and access the diagnostic information. By cross-referencing the error codes with an online trouble code library, you can potentially identify the reason for the specific issue.

  • Fuel Level Sensor Circuit Intermittent (P0464)
  • Fuel Level Sensor Circuit High Input (P0463)
  • Fuel Level Sensor Circuit Low Input (P0462)
  • Fuel Level Sensor Circuit Range/Performance (P0461)
  • Fuel Level Sensor Circuit Malfunction (P0460)

Several codes may be encountered, some of which indicate electrical faults. It is possible that a faulty connection or ground could be responsible for these codes. Additionally, if you refuel your car while the engine is operating, it can cause a rapid change in fuel levels, triggering these codes.

By utilizing a scanner and referring to the trouble code library, you can gather valuable information about the cause of the check engine light. However, it’s important to note that interpreting the codes accurately may require the expertise of a qualified technician for the proper diagnosis and resolution of the problem.

2) Inspect the Fuel Gauge Fuse

If your fuel gauge is not functioning at all, a good starting point is to check the fuse. A blown fuse may stop your vehicle’s fuel sending unit from working.

Replacing a blown fuse is a simple task. Ensure that you select a replacement fuse with the same amperage rating as the one being replaced.

3) Run a Self-Test

Modern vehicles often perform self-tests to diagnose various systems. The vehicle manufacturer can provide a specific procedure for conducting a self-test on the electronic fuel gauge. Consult a service manual to find instructions on how to perform this self-test.

Start a self-test that runs through the instrument panel display and gauges. When conducting the test, observe if the fuel gauge successfully transitions from a full reading to an empty indication.

If the fuel gauge fails to demonstrate this expected behavior during the test, it is probable that the gauge itself is at fault rather than the fuel sending unit. In such cases, additional troubleshooting or repair procedures may be required to address the underlying gauge-related issue.

4) Use a Multimeter

If there is a poor connection in the signal wire or an inadequate ground wire connection to the fuel sending unit, it can lead to wrong fuel readings. To address this issue, refer to the service manual and follow the given method to disconnect the instrument cluster from the dashboard.

Inspect the fuel gauge wire, and if it appears undamaged, use a multimeter set to 20V DC to measure its voltage. The gauge must get 12V of power, so if it falls short, trace the wires to check for any signs of corrosion or damage.

Next, proceed to test the fuel sending unit located in the gas tank. Check for indications of damage or corrosion, and ensure that the unit is correctly seated in the tank.

If your unit appears dirty, cleaning the connectors can help expand connectivity. To measure the voltage, set the multimeter to 20V DC and compare the reading with the specifications provided in the vehicle service manual to verify its accuracy.

5) Check Ohms

If all previous inspections yield satisfactory results, it is time to examine the Ohms of your fuel sending unit. To do this, your unit must be extracted from the gas tank to allow easy manipulation of the float arm. Refer to the procedure outlined in your vehicle’s repair manual to perform the Ohms or resistance check.

If the Ohms reading aligns with the expected values, but your fuel gauge still fails to display the correct fuel level, it indicates a wiring problem between the fuel sending unit and the gauge. Conversely, if the Ohms reading is incorrect, it signifies a faulty fuel gauge sender that needs to be replaced.

How To Replace Fuel Sending Unit

Follow the below given step to replace your fuel sending unit:

  • Depressurize the fuel tank.
  • Disconnect the electrical connections and fuel lines linked to the fuel sending unit.
  • Thoroughly clean the area around the plug to prevent any contaminants from entering the tank.
  • Remove the retaining ring securing the fuel sending unit.
  • Carefully extract the fuel sending unit from the tank, ensuring the O-ring or gasket comes out with it.
  • Compare the removed unit with the new one to verify that it is an exact replacement.
  • Install the new unit in its designated position, ensuring a fresh O-ring or gasket is in place.
  • Securely align the gasket between the tank and the fuel sending unit.
  • Reconnect all wiring connections.
  • Attach and secure the fuel lines into their proper positions.
  • Inspect for any fuel leaks.

If you want to perform this task yourself, it is essential to have a fire extinguisher nearby. Avoid working in the vicinity of potential ignition sources, and ensure you wear appropriate safety gear. If you have concerns about working on the fuel system, it might be advisable to enlist the services of a mechanic.

Fuel Gauge Sender Replacement Cost

The replacement cost of the fuel sending unit depends on the vehicle model and labor cost. The average replacement cost of the fuel gauge sender is between $700 and $1,400. The fuel sending unit itself costs from $120 to $280.

FAQ Section

Will any fuel gauge work with any sending unit?

It’s important to note that sending units may not be universally calibrated, especially when dealing with aftermarket parts and OEM fuel gauges. Therefore, it is crucial to ensure compatibility between the components before replacing the sending unit to avoid potential issues.

Can a car run with a bad fuel sending unit?

A malfunctioning fuel sending unit can’t prevent your vehicle from running as long as there is gas in the tank. However, the challenge lies in accurately knowing the fuel level during this fault. By manually tracking the fuel in the tank, you can easily drive for a short period without finishing off fuel.

How do I reset my fuel sending unit?

To reset the fuel sending unit, refer to the procedures outlined in the repair manual. It can instruct you to switch on the ignition and push the odometer or trip button. Following this, turn off the ignition and hold down the trip button for 2s, then release and press it again, replicating the process 3 or 4 times. At the last, hold down the button until the data is displayed on the odometer.

Will disconnecting the battery reset the fuel gauge?

Resetting the fuel gauge can sometimes be achieved by removing the battery momentarily. But it’s important to note that disconnecting the battery will also reset other settings, such as radio presets and seat memory functions, which may require reconfiguration.

What are the fuel sender unit problems?

A malfunctioning fuel sending unit can lead to sudden and erratic movements of the gauge needle or provide inaccurate readings. For example, the gauge may initially show three-quarters full and then, within a few minutes, suddenly drop to half full, or vice versa; it may initially indicate a full tank and then gradually climb higher shortly after.

Can a fuel sending unit cause a misfire?

A defective or failing fuel pump can cause a lean air-fuel mixture characterized by an excessive amount of air and insufficient fuel. This imbalance can lead to issues such as misfires, which occur when combustion is incomplete and can result in engine performance problems.

Can a bad fuel sending unit cause rough idle?

The fuel injection system plays a vital role in starting your car by delivering the correct mixture of air and gasoline to the engine’s cylinders. If the fuel injectors become clogged or gummed up, they may fail to provide the proper ratio of fuel and air, resulting in symptoms such as a rough idle or sluggish acceleration.

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