- 1 Common causes of fuel gauge malfunction
- 2 1. Bad fuel gauge sender
- 3 2. Electrical faults
- 4 3. Fuel gauge failure
- 5 4. Instrument cluster failure
- 6 Symptoms of a bad fuel gauge sender
- 7 How the fuel gauge sender unit works
- 8 1. Fluctuating fuel gauge
- 9 2. Fuel gauge gets stuck on empty
- 10 3. Fuel gauge gets stuck on full
- 11 4. Fuel gauge drops and gets stuck at half tank
- 12 How to fix electronic and software malfunctions
- 13 How to reset your fuel gauge (ECU)
- 14 Tip
- 15 NB
Is your fuel gauge constantly fluctuating? Does it get stuck sometimes? Or is the pointer failing to drop below a certain point even when your tank is going empty? If any of the above is the case, it means your fuel gauge system needs be be fixed urgently.
The fuel gauge gives you information on how much fuel is left in your tank and alerts you when it is time to top-up some more fuel. A malfunctioning fuel gauge may cause you to run out of fuel unexpectedly, and this can put you in a really dangerous situation. However, that may seem like a relatively minor inconvenience compared to the long term consequences running completely out of fuel may have on your vehicle. Running low on fuel can lead to fuel pump wear, and fuel pump overheating. It can also cause the fuel pump to pick up sediments, which clog the fuel filter, fuel injectors, or high pressure fuel pump.
If your fuel gauge isn’t giving you accurate information, it’s important to identify the source of the issue, then make a plan for repair.
Some fuel gauges have an analog display while others have a digital or liquid crystal display. Read on to learn the most common causes of malfunctioning fuel gauges and how to fix them.
Common causes of fuel gauge malfunction
The fuel gauge system can be broken down into three basic parts: gauge, sender, and circuit. A fault in one or more of these parts will lead to a fuel gauge failure.
The fuel gauge is a relatively simple circuit, but its simplicity means each component is essential to its function. Here are some of the most common ways that the fuel gauge can fail.
1. Bad fuel gauge sender
This is the most-common cause of a fuel gauge not working. When the vehicle is in motion, the sending unit is in constant motion, constantly rubbing the variable resistor. Over time, the contacts can wear, leading to an open circuit. The fuel gauge might interpret voltage feedback from a dead sender as FULL or EMPTY, consequently pegging the gauge no matter the actual fuel level.
2. Electrical faults
Circuit Problems can cause the fuel gauge to stop functioning normally. Depending on the location of the fault, the fuel sender may not have a source voltage, the fuel gauge may have no fuel sender voltage, or the ground for either one may be interrupted. Loose connections and corrosion can also cause problems, particularly at the Fuel Pump Module, which is usually exposed to the elements.
3. Fuel gauge failure
This is less common, but still a possible issue. If the internal circuit is faulty, the fuel gauge may only function in one section, such as between HALF and FULL or between EMPTY and HALF. If the internal circuits are shorted, they may peg to FULL or EMPTY. If the circuit is open, the gas gauge will likely sit at EMPTY and never move.
4. Instrument cluster failure
This is the least common, and likely the most expensive problem to fix. Modern instrument clusters are fully-integrated circuits and may not even feature replaceable bulbs. If the gas gauge fails as part of the cluster, the whole unit must be replaced.
Symptoms of a bad fuel gauge sender
As a result of its constant motion in the fuel tank, the fuel gauge sender stands a better chance to wear-out more quickly than the other components of the fuel gauge system. A bad fuel gauge sender is undoubtedly the most common cause of a malfunctioning fuel gauge system. Here are some indicators that a fuel gauge sender is has began to wear-out and needs a replacement.
1. Erratic fluctuations of fuel gauge
2. Gauge gets stuck on empty
3. Guage gets stuck on full
4. Pointer/reading drops and gets stuck at a half tank
But before we go into the diagnosis of each symptom and the likely faults, it is important to understand how the fuel sender unit works.
How the fuel gauge sender unit works
The fuel gauge sender is a component that is found in the gas tank of most road going vehicles. The fuel gauge sender, also commonly referred to as the fuel sending unit, is the component responsible for sending the signal that operates the fuel level gauge in the instrument cluster. The fuel sending unit is made up of an arm, float, and a resistor that changes according the position of the float. The sender float is designed to float on the surface of the fuel inside of the tank. As the level drops, the position of the arm and float will shift and move a resistor which controls the display on the gauge. When the fuel sending unit has an issue it can cause the vehicle to experience issues with the fuel gauge, which can put the vehicle at risk of running out of fuel. Usually a bad or failing fuel gauge sender will produce a few symptoms that can alert the driver of a potential issue.
1. Fluctuating fuel gauge
One of the first symptoms of a problem with the fuel gauge sender is a fuel gauge that behaves erratically. A faulty fuel gauge sender may cause the gauge to suddenly change positions, or give an inaccurate reading. The gauge may appear to be at three quarters, and then only a few minutes later will change to half full, or vice versa the gauge may appear to be full, only to have the gauge climb higher a short while later.
2. Fuel gauge gets stuck on empty
Another common symptom of a faulty fuel gauge sender is a gauge that is stuck on empty. If the float somehow breaks or becomes separated from the arm it may cause the fuel gauge to malfunction and become stuck on empty. A faulty resistor can also cause the gauge to read empty.
3. Fuel gauge gets stuck on full
Another, less common, symptom of an issue with the fuel gauge sender is a fuel gauge that is stuck on full. A faulty fuel gauge resistor can send a bad signal to the instrument cluster which can cause the gauge to permanently read full. This is an issue, as the driver needs to know the accurate fuel level of the vehicle as to not run out of fuel.
4. Fuel gauge drops and gets stuck at half tank
This is the most common symptom of a faulty fuel gauge sender. The fuel gauge gets stuck and doesn’t go below a certain point even when the tank is going empty. If more fuel is added, the gauge will go up but as the gas is been used up, the pointer stops and stay on half. This could be as a result of a float hanging up inside the tank or bad level sensor.
How to fix electronic and software malfunctions
Electronic and software malfunctions may also cause the fuel gauge in your automobile to inaccurately measure or display the amount of fuel remaining in the gas tank. If this happens, it means you can reset your fuel gauge by clearing off the memory in the program that controls your fuel gauge in the Electronic Control Unit of your car. Each make and model of car has its own specific instructions on how to reset the fuel gauge, but the process is basically the same. To reset your fuel gauge, follow the steps below.
How to reset your fuel gauge (ECU)
1. Turn the ignition switch to the “On” position.
2. Press the “Odo/Trip” button until the odometer is put into “ODO” mode.
3. Turn off the ignition.
4. Press and hold the “Odo/Trip” button. Turn the ignition switch to the “On” position. Hold the “Odo/Trip” button for two seconds. Release the “Odo/Trip” button and then immediately press it again, release it, press it, release it and then press it and hold it. Hold the button until the leveling information is displayed on the odometer, about five seconds.
5. Release the “Odo/Trip” button.
6. Press and hold the “Odo/Trip” button until the odometer display reads “1”, which indicates the reset process has begun.
7. Release the “Odo/Trip” button when the reset process is complete, which is indicated when the odometer display returns to normal.
8. Turn off the ignition.
The above instructions are based on a Toyota Prius and other Toyota models. Consult your automobile’s owner’s manual for specific instructions on how to reset the fuel gauge on your make and model of car.
If the fuel gauge fails to reset to normal, you are advised to urgently schedule a fuel guage sender replacement.
The fuel sending unit is not a routinely serviced component, usually only serviced when it, or the fuel pump fails, however it does play an important role to the proper operation of the vehicle. If you fuel gauge is displaying any of the symptoms, or you suspect that there may be an issue with this unit, have the vehicle inspected by a professional technician.