Not being able to start your car is the worst thing that can happen. Even more annoying is when a jump start doesn’t fix the problem.
The good news is that just because your car’s battery isn’t dead doesn’t mean you have to deal with a costly problem. If your car has a lot of miles on it and won’t start, it could be because the fuel relay is broken.
How can you tell if that’s your problem, and what do you need to do to fix it? There are some clear signs that a fuel pump relay has failed, and it’s easy to find out if one has. Keep reading our guide to find out!
What is a Fuel Pump Relay?
A relay is an electrical switch with a fancy name, but it doesn’t work like a light switch. Instead, the relay is controlled by your car’s ECU, which turns it on and off when it needs to.
The fuel pump relay controls the power to the fuel pump, which is an important part of the engine of your car. Because of this, if your fuel pump relay is broken, you probably won’t be able to start your car, and if you do, it will be hard to keep running.
Relays don’t break as often as fuses, but they can if there is a short in your system or if your car has more than 100,000 miles on it. Like every other part in your car, the more you use it, the more likely it is to break.
Why Your Fuel Pump Relay Matters
If your engine doesn’t get fuel, you’ll never be able to start it. Your fuel pump pulls fuel from your tank and sends it to your injectors, but if it doesn’t have power, it won’t do anything.
But if your fuel pump keeps running all the time, you’ll flood your engine and it won’t run right either. So, your fuel pump needs to be able to easily turn on and off. That way, your engine will run at its best.
So, your fuel pump relay is what you need. It shuts off and starts your fuel pump quickly and easily when your engine needs it. It gets its orders from the ECU, which uses information from all of the engine’s sensors to figure out when the fuel pump needs to run.
So, why should you care about your fuel pump relay? Because if you don’t have it, you’ll never be able to get out of the driveway and onto the road.
Symptoms of a Bad Fuel Pump Relay
It’s easier than you think to figure out what’s wrong with a fuel pump relay. There are a few telltale signs that you should look into something more. And once your car shows these signs, it’s easier than you think to test your fuel pump relay.
A fuel pump relay can break in two ways. It can get stuck either in the “off” or “on” position. If you can start your engine, but it won’t keep going, it might be because the fuel pump relay is stuck in the “on” position.
This is because your fuel pump is sending too much fuel to the injectors, which causes your engine to flood. In spite of what you might think, putting too much fuel in your engine won’t make it go faster or blow up. Your engine won’t be able to handle it, and it will probably just stop working.
Even though a stuck-on fuel pump relay happens less often than a stuck-off one, it does happen. If your engine keeps stopping, you should check your fuel pump relay to see if that’s the problem. It’s easy and quick, and it could save you a lot of money.
The best part is that you don’t have to take apart your engine to try to find a deeper problem before you rule it out!
Engine Does Not Start
This happens a bit more often than your engine stops running. If your fuel pump relay is stuck in the off position or has burned out, you won’t be able to start your engine. This is because there won’t be any fuel going from the tank to the cylinders, and the engine won’t start.
You will still be able to hear your engine start up, which could make it hard to hear anything else inside the car. Even if your engine won’t start and your battery is fine, that doesn’t mean the fuel pump relay is the problem. However, it is one of the easiest things to rule out.
Before you try to fix the fuel pump relay, check out number 3 on our list if your car won’t start.
No Noise from the Fuel Pump
This goes right along with number two. If you try to start your car but don’t hear the fuel pump turn on, there are probably two things wrong. Either you have a bad fuel pump or a bad fuel pump relay.
Checking your fuel pump relay is the easiest and cheapest thing you can do in this situation. Even though you might need a new fuel pump more likely, the relay is much cheaper and easier to check.
Make sure the fuel pump is getting power before you order a new one. If the fuel pump relay is not the problem and the fuel pump is getting power, you probably need a new fuel pump.
Check Engine Light
If the fuel pump relay is stuck in the off position on a newer engine, the check engine light might come on. However, on most engines, the check engine light will only come on if the fuel pump relay is stuck sending power to the fuel pump.
That’s because the check engine light comes on when one of your engine’s sensors gives the ECU a wrong reading. This means there is a problem, so the check engine light comes on.
But if your fuel pump doesn’t turn on, it’s not likely that a sensor is giving you a wrong reading. So, if your fuel pump relay is stuck in the off position, you probably won’t get a check engine light.
How To Find Your Fuel Pump Relay
Your fuel pump relay will be in the fuse box of your car. They are usually square and black, with no other marks to make them stand out. If your fuse box has a cover, look inside to see if there are any labels. If it is, you’re lucky! All you have to do is look on the cover for the fuel pump relay and find it in the fuse box.
But not every car has a fuse box with a label right on the cover, even though every car should! If you own a car that doesn’t have a fuse box cover with labels, you can do one of two things.
The first thing you can do is try to find a diagram in the owner’s manual for your car. Again, not every car’s manual will have a diagram (chart). But if you are a car engineer and you are reading this, you should put one there!
The Internet is another place you can look for a diagram. It’s not always easy to find, but if you’re having trouble, chances are other people have too. The good news is that mechanics are usually pretty good about sharing what they’ve learned, and there are a lot of forums with this kind of information.
You might have to look through a few forums to find it, but the diagram you’re looking for is probably out there. If you can’t find it online, you’ll have to contact a dealer and see if they can help. Sometimes they will, sometimes they won’t, and sometimes they will charge you for it.
How Can you Test for a Bad Fuel Pump Relay?
You can check for a bad fuel pump relay in three ways. One is the right way, and the other two are easy. But here’s a spoiler: this eight-year-old mechanic uses the easy ways and has never made a mistake with a relay.
Before using any of these methods, you need to make sure that your relay is getting power. No matter how much you try to fix relay problems, if the wiring doesn’t have power, the relay won’t work.
Swap the Relay with Another One
It’s the easiest way to tell if your fuel pump relay is broken. When you open your fuse box, you’ll see that the fuel pump relay looks the same as 4-6 other relays. Because they are the same, they look the same. They both have the same OEM part number and perform the same function.
It makes it very easy to check if a relay is broken. Find a working system, switch the relays, and see if the problem moves. If it does, your relay is broken. If it doesn’t, the problem isn’t with your relay.
Of course, this only works if the relay gets power to begin with. If it’s not getting power, a good relay can’t do anything.
Use a 6 Volt Battery
Every mechanic has used this old trick, but it doesn’t always work. All you have to do is connect the positive and negative ends of the battery to two of the posts on the relay. If you hear a click, the relay is working perfectly. If you don’t hear the relay click, it’s probably broken.
But this method doesn’t always work. Even though the relay wasn’t made to work on 6 volts, most of them will anyway. There’s also a small chance that the relay isn’t fully engaged or doesn’t stay engaged.
If your relay doesn’t click over with a 6-volt battery, it’s almost certainly broken. If it does click over, it’s almost certainly fine.
Most relays will have four or five posts as well. For it to work, you have to connect the right two. You can figure it out by looking at the diagram on the relay or by trying all the possible combinations until you find one that works.
You don’t have to worry about burning out the relay if you hook it up wrong. The 6-volt battery isn’t strong enough to break the relay unless it has major problems.
Check for Resistance
Do you remember how we said that a 6-volt battery only works 99 percent of the time? Every time you check for resistance, it works. To see if your relay is working right, you will need a multimeter or another tool for testing resistance.
Checking to see if there is a short in the system is the first step. All you have to do is check for continuity between the power terminal and the other power terminal. If you see a number other than “OL,” which stands for “open load,” “infinite,” or “out of limits,” you have a shorted relay and need to replace it.
Then, connect one jumper wire from the power circuit terminal to the positive post on your battery. Connect a second wire from the terminal of the control circuit to a good ground. You should be able to hear your relay change. If it doesn’t, the relay is broken.
If it does, you still have to check for resistance. It would help if there wasn’t much or any resistance. If not, the relay is broken and needs to be changed.
Why do Fuel Pump Relays Break?
Your fuel pump relay could have broken because of a surge in the system, but it’s much more likely that it’s just old. Just like any other part of your car, your fuel pump relay can wear out after a lot of use.
The metal posts can rust, or the switch inside the relay can break off. Even though relays are pretty simple and don’t break very often, it does happen. Usually, it’s just because of age. Switch out the relay and keep going.
Can You Drive with a Bad Fuel Pump Relay?
Not even close. If your fuel pump relay is broken, your engine will either flood or won’t start at all. That means you’re going down a rabbit hole if you worry about your fuel pump relay because your engine isn’t running as well.
Look elsewhere for your problem.
How Expensive is a Fuel Pump Relay?
So, you found out that the part that was giving you all those problems was your fuel pump relay. Your fuel pump relay is one of the cheapest parts in the whole system, which is good news. Fuel pump relays aren’t as cheap as fuses, but they usually cost between $20 and $50.
Even better, fuel pump relays are easy to get to, so changing them shouldn’t cost much in terms of labour. The only thing the mechanic might charge extra for is the time it takes to figure out what’s wrong.
But if you know that you need to change your relay, it shouldn’t take the mechanic more than 15 minutes to do the whole job.
For a small piece of plastic and metal, $20 to $50 might seem like a lot of money. Just be thankful that it wasn’t the gas pump. Most of the time, they cost between $100 and $200 and are a lot harder to get to.
How Hard is it to Replace a Fuel Pump Relay?
The fuel pump relay is one of the easiest parts to change in your car, as long as you can get to the fuse box. If the relay is really stuck, you might need pliers, but otherwise, all you have to do is find the right relay, pull it out, and put the new one in.
To keep the terminals from rusting, you should put a little dielectric grease on them. But don’t use too much grease. If you do, it could get into a terminal that isn’t sealed, which could cause your relays to fail too soon.
How Often do Fuel Pump Relays go Bad?
It doesn’t happen often, but it does. But it happens so rarely that if it does happen once to your car, the repair should last for the rest of the car’s life.
But if you’re troubleshooting a car that won’t start, there are probably other things going on. But fuel pump relays are easy to check, so that should be one of the first things you do, even if it’s not the most likely cause.
Other Things to Check if Your Fuel Pump Relay is Good
Even if your fuel pump relay works, there are a few things that could be stopping your car from starting. We’re going to stick with the fuel system for this list, but your problems could be caused by other things as well.
The Fuel Pump
It is one of your fuel system’s most expensive parts. It’s one of the most likely to break, which is a shame. Your fuel pump has a lot of moving parts, and if any of them stop working, you won’t be able to start your car. If you can’t hear the fuel pump turning on, you’ve ruled out the relay, and you have power, it’s likely that you need a new fuel pump.
A Blown Fuse
If you checked for power and found none, it’s likely that a fuse has blown somewhere. It’s the cheapest problem you could have, but if the car has a short in the system, you’ll need to find it and fix it or you’ll blow a lot of fuses.
There’s Air in Your Fuel System
If your car ran out of gas or you just changed parts in the fuel system, like the injectors or fuel pump, you might need to get the air out of the system. If there is air in your engine, it won’t work the way it should.
To get your car to run again, you’ll need to crack the injectors to purge the system. It’s free if you can do it yourself. If not, a mechanic will need a few hours to fix it. They won’t have to order any parts, though.
If your problems started right after you left the gas station, your fuel might be the problem. Sometimes you get a bad batch, but it’s more likely that you used the wrong kind. Diesel won’t work at all in a gas car, and gas won’t work at all in a diesel car.
Now, if you try to start a car that has been sitting for a few years, the fuel has probably gone bad. Before you can get anything to run again, you’ll need to empty the tank, flush the system, and put in new fuel.
Again, you don’t need any parts to do this, but it does take a little time.
Fuel pump relays that don’t work right can be a real pain to fix. Often, inexperienced or do-it-yourself mechanics will skip over the relay and go straight to more expensive parts like the fuel pump or injectors.
Before you order any of those parts, check your fuel pump relay. Even if it’s not likely to be a problem, it’s much easier and cheaper to check than those other parts. It might seem like a waste of time, but it could save you a lot of money and a lot of trouble.