One gauge in your dashboard that you pay attention to more than you realize is the fuel gauge. It’s an important part of keeping your car rolling down the road, and you probably take it for granted. But behind every fuel gauge, a fuel sending unit does its job.
So how do you know when a fuel sending unit is on its last legs, what makes it fail, and what it might set you back to replace it?
What is a Fuel Sending Unit?
The fuel sending unit has a few different names. Other common names include fuel level sending unit, a fuel gauge sender, and even a float gauge.
Whatever you call it, the fuel sending unit sends a signal to the fuel gauge in your vehicle to let you know how much fuel is currently in the tank.
Bad Fuel Sending Unit Symptoms
If you have a bad fuel sending unit, there are some classic signs you can’t miss. But while these symptoms are pretty clear and easy to spot, you need to rule out a faulty fuel gauge before you decide to change out the fuel sending unit.
#1. Erratic Fuel Gauge.
If the fuel gauge is all over the place and can’t seem to settle at one reading, it may have a malfunctioning fuel sending unit. This can be caused by the float gauge moving around more than it should, or the variable resistor in the fuel sending unit is not working correctly.
When this happens, it can lead to very erratic behavior at the fuel gauge as the signal coming from the fuel sending unit is all over the place.
#2. Incorrect Fuel Gauge Readings.
Whether you just filled up the tank or you’re running low, the fuel gauge should tell you just how much gas you have. If the reading doesn’t match what’s in the tank, the gas sending unit could be the culprit.
Just remember, the problem could also be the fuel gauge, so it’s wise to test the sender before replacing it.
#3. Stuck Fuel Gauge.
A fuel sending unit may often fail by getting stuck in a particular position. When that happens, your fuel gauge will not register any changes, whether the fuel tank is full or empty!
At times, the fuel sending unit will get stuck; it will record empty, but it may be full, or it might be stuck in some position. When it comes to a stuck or inaccurate fuel gauge, diagnostic codes P0460 and P0463 may trigger your car to light up its check engine light in some cases.
What Causes the Sending Unit to Fail?
The main reason a fuel sending unit goes bad is simply age. The component in the fuel sending unit most susceptible to failure is the variable resistor.
Over time, the resistor can begin to gunk up from fuel, or it can start to corrode. Even the subtlest of changes can affect the fuel sending unit.
Another possibility is that something gets lodged between the variable resistor and the metal rod, holding it in place so that it cannot move. If this happens, the fuel gauge will always read the same amount, regardless of how much fuel is in the tank.
One way to avoid this from happening is to only ever fill the car with high-quality fuel, but at some stage, the metal rod can become corroded and stuck in one place.
How Does a Fuel Sending Unit Work?
A fuel sending unit is made up of three components. The first being the “float.” The float is a simple piece of rounded or oval buoyant material that won’t fall apart in fuel.
The float connects with the second part of the fuel sending unit, the metal rod. With the metal rod, the name says it all. It’s a thin metal rod that connects the float with the variable resistor. The important thing with the metal rod is that it is flexible, to be able to move with the float.
The float should always sit on top of the fuel. The metal rod moves out of the way to allow the float to move to the right position inside the gas tank, depending on how much fuel is currently in there.
And the last part of the fuel sending unit is the variable resistor. The variable resistor receives a very small signal voltage coming from the vehicle battery, and depending on the fuel level of the vehicle it adjusts its resistance to reduce the signal.
The vehicle’s computer receives this and converts the voltage to a fuel percentage so that it knows what to show on the fuel gauge.
Here’s a short video on how this all works:
Sending Unit vs Fuel Pump
When some drivers hear the phrase fuel sending unit, their thoughts may drift towards a fuel pump.
This is due to the fact that “sending” in a fuel sending unit is somewhat of a misnomer. A fuel sending unit does not send any fuel, it sends a signal indicating how much fuel is in the tank.
The fuel pump sends the fuel that the computer requests to the combustion chamber, the fuel sending unit has no part in that. All a fuel sending unit actually does it tell you how much fuel is in the fuel tank!
Fuel Sending Unit Replacement Cost
If you’re taking your car to a garage to have them replace the fuel sending unit, you can expect to pay somewhere in between $900 and $1,100 for the repair. If you’re willing and able to do the work yourself, you can save yourself quite a bit of money.
That’s because the price of a new fuel sending unit is normally only between $150 and $200. The rest of the costs are just labor. Labor for this job runs from $800 to $900.
The job is labor-intensive but the major thing for DIY mechanics is that you need something to hold up the gas tank while you drop it down and then get it back up and secured. You’ll have to disconnect every fuel line.
All in all, it’s not that hard of a job, but it is time-consuming and it’s best to support the tank with a hydraulic jack.