Fuel Sending Unit Buyer's Guide
- The fuel sending unit, also known as fuel level sensor, fuel tank sending unit, and fuel gauge sender, is a potentiometer found inside your vehicle’s fuel tank.
- The fuel sending unit changes according to the position of the float, depending on the level of fuel in the tank.
- Symptoms of a faulty fuel sending unit
- Fluctuating fuel gauge readings
- Fuel gauge indicates full at all times
- Fuel gauge always on empty
- OE replacement fuel sending units typically cost around $10 to $610.
- When replacing the fuel sending unit with an OE replacement, make sure both component matches in terms of ohms.
Your fuel gauge tells you how much fuel is left in your gas tank. It’s the analog or digital device found incorporated in your instrument panel. This component measures the level of fuel so you would know when to fill up. But have you ever wondered how these amazing devices work? A good start in finding out how the fuel gauge works is learning about the actual mechanism that sends information about your fuel level to the gauge—the fuel sending unit. Let’s find out what does a fuel sending unit do and how important it is in measuring your fuel level.
What is a fuel sending unit?
The fuel sending unit, also known as fuel level sensor, fuel tank sending unit, and fuel gauge sender, is a potentiometer found inside your vehicle’s fuel tank. This assembly is usually a part of the fuel pump module along with other fuel delivery components. A fuel sending unit consists of a foam float that’s connected to a metal rod called the arm, which is then mounted to a variable resistor. A resistor is an electrical device that resists electric current.
The fuel sending unit changes according to the position of the float, which, on the other hand, depends on the level of fuel in the tank. When you fill up your gas tank, the float connected to the metal arm rises. The arm then slides a moving contact along the variable resistor. If the resistance reaches a certain point, the sending unit will trigger the low fuel light on the instrument cluster by sending an electric current to the fuel indicator.
Apart from the fuel sending unit, a vehicle’s fuel pump module consists of two more parts. In able for your gauge to work, it needs to have all three working together smoothly. The other two components of this assembly are the fuel pump and fuel strainer. The keyword for determining the actual fuel level measurement is resistance, and the sender unit needs to have all components working properly for an accurate reading.
Symptoms of a faulty fuel sending unit
The fuel sending unit is essential in keeping track of your fuel level. Without it, you may end up draining your fuel tank halfway to your destination—which is also as bad as having a malfunctioning one. It is important to be vigilant about the issues your car may face along the way so here’s how you can tell if your fuel sending unit badly needs a replacement.
Fluctuating fuel gauge readings
One of the few common symptoms of a failing fuel sending unit is a fuel gauge that behaves inconsistently. You can observe this by paying attention to your gauge as you drive short distances. Your gauge may show half before you drive off the driveway then a minute later it could drop by a quarter or rise to almost full. The inaccurate reading could result to you having to fill up irregularly.
Fuel gauge indicates full at all times
A fuel gauge that is stuck on empty is often a result of a disembodied float. Without the float, the metal rod arm won’t be able to move and rub the variable resistor. If the fuel sending unit can’t transfer electric current to the gauge, the Moylan arrow (if your car features an analog fuel gauge) will not move. If the arrow’s position was on empty before the float got separated from the arm, it will stay there until you let a mechanic fix or replace your fuel level sensor.
Fuel gauge always on empty
If your gauge always reads full, it maybe due to a faulty variable resistor. A damaged or malfunctioning resistor can send bad signals to your gauge, which could result to the Moylan arrow always pointing to full.
Keep in mind that the fuel level sensor is not part of a maintenance routine. You only need to have it checked if you experience one of the aforementioned symptoms. Even if you can DIY-check the sender unit, we still advise that you go to a certified mechanic.
Faulty fuel gauge? Your fuel sending unit might have an issue
Your vehicle’s gas gauge is a simple component but like any other component, it could face issues. Here are some causes of fuel gauge failure.
Fuel sending unit problems
If your gauge appears to be malfunctioning, the first component you want to look at is the fuel tank sending unit. This could be due to wear and tear in the sender unit’s moving part. When your vehicle is in motion, the fuel tank sending unit constantly moves as well, rubbing the variable resistor. The contacts could wear over time, which could often lead to an open circuit somewhere in the system. As a result, the fuel gauge could give you inconsistent reading of your fuel level.
Loose circuit connections and short circuit
Loose connections are common fuel sending unit problems that have been encountered by drivers with faulty gas gauges. Faulty internal circuit could render to loss of source voltage that could affect the fuel sender, interrupted ground, or half-working fuel gauge. Short circuit is a culprit for gas gauges that only works in one section, which could either be from half to full or empty to half.
Corrosion can form inside the fuel pump module, which affects its performance. The fuel pump module is naturally exposed to contaminants due to fuel additives like alcohol. When corrosion starts to form inside the fuel pump module, you could face unreliable fuel gauge readings.
Instrument panel failure
Probably the most expensive causes of a fuel gauge failure, an instrument panel failure may require you to replace the whole assembly. Most modern instrument panels feature fully-integrated circuits. Good thing, cases of instrument panel issues causing the fuel gauge to malfunction are rare.
How much is an OE replacement fuel sending unit?
OE replacement fuel sending units typically cost around $10 to $610. They are sold individually, as an assembly, or as part of a kit. You also need to determine the location of installation, as there are items that feature specific installation location. Some fuel level sensors are installed in the side, rear, midship, or front tanks. For proper installation, we recommend seeking a certified mechanic’s help when replacing a faulty sender unit.
What to consider when replacing a fuel sending unit
It is very important that your fuel sending unit is compatible with the gauge installed on your vehicle. So, when replacing the fuel tank sending unit with an OE replacement, make sure both component matches in terms of ohms. Ohm is the SI unit of electrical resistance, which is crucial in measuring your fuel level. There are different ohm values but the common ones are 0-90, 73-10, 240-33.5, 0-30, and 16-158 ohms. You’ll have to know these, especially when replacing your existing sender unit, though there are also universal fuel sending units in the market.
Replacing the Fuel Sending Unit
You can change your vehicle's fuel sending unit in these few steps:
Difficulty level: Moderate
Things you'll need:
- Fuel container / gas container or catch pan
- Ratchet and socket
- Racket extension
- Drift punch
- Hand siphon pump
- Set of wrenches
- New sending unit rubber seal
- Car's repair manual
Step 1: Detach the fuel pump relay. Start the engine and wait for it to stall. Refer to your car's manual to find the fuel pump and to learn how to relieve the fuel system pressure properly.
Step 2: Return the fuel pump relay to its position and remove the ground battery cable using a wrench.
Step 3: With a hand siphon pump and a fuel container, empty the fuel tank through the tank filler neck.
Step 4: To remove the fuel sending unit, lift the rear of your car with a floor jack and secure it on jack stands. Consult your car's manual to see if your vehicle has access to the fuel sending unit through an access door underneath the rear seat.
Step 5: Use a ratchet, a ratchet extension, and a socket to unbolt the tank straps. Lower the tank a few inches and disengage the fuel lines and hoses. Unlock the hose plastic connectors and disconnect the hoses from the sending unit's assembly fittings.
Step 6: Disconnect the fuel pump electrical connector and put the fuel tank on the floor.
Step 7: Unbolt the cam lock holding the sending unit to detach it from the tank. Twist the lock counterclockwise using a drift punch. Take out the sending unit assembly and throw the rubber seal away. Then detach the fuel pump from the old fuel sending unit.
Step 8: Proceed with installing the fuel pump on the new sending unit. Installing the new sending unit is the reverse of removing the old sending unit. Just do the previous steps backwards, starting with returning the sending unit's cam locks.