A faulty fuel pump relay can be a hassle or inconvenience for any driver. This small electrical component is an important part of your engine’s starting and operation, and a failed relay can leave you stranded.
In this guide, we’ll go over symptoms of a bad fuel pump relay, how to diagnose it, and suggestions for repairs and/or replacement.
What is a Fuel Pump Relay?
When you turn the key or push the start button on your vehicle, there is more happening than you typically think. One of the things that is happening is that your vehicle’s ECM is sending a signal to your fuel pump that tells it to send the right amount of fuel into the combustion chamber for the engine to start.
The way the ECM does this is through controlling a relay, the fuel pump relay. When the current to the fuel pump relay reaches a certain point, it switches, connecting the fuel pump to the power source. When it does not switch, the fuel pump gets shut off, and the engine does not receive fuel.
The “at rest” condition for the fuel pump is off, which is a good thing, otherwise, you’d run out of fuel all the time! Since the fuel pump relay is like a door between the ECM and the fuel pump, it is an important component!
Key Takeaway:
- The fuel pump relay is an electromagnetic switch that uses low current to control a larger current circuit.
- Common signs of a failing pump relay are ignition problems, the fuel pump runs continuously, or a check engine light.
- The average cost of a Fuel Pump Relay Replacement is between $67 and $75. Average labor costs are between $30-$38, and average parts are $37.
Location
Having checked under the hood and the dashboard, you’ve managed to locate the fuel pump relay. The exact placement will be different depending on what you drive, but there are two common places to look; those two places are:
- The bottom of the hood by the firewall or
- The bottom of the dashboard on the passenger side.
The fuel pump relay will not have big flashing lights telling you what it is; however, if you are fortunate, there may be a diagram attached to the underside of the fuse box outlining what each of the relays and fuses is.
If there isn’t a diagram on the fuse box, now you’ll have to do some online searching to determine which relay is the fuel pump relay.
Function
Turning the key to start your car begins the “start cycle” of the combustion engine, evident in this sense of relay as the switch closes and the fuel pump relay is activated long enough to provide a current to start the fuel pump.
Consistent voltage is needed for the fuel pump, which is the key. When the engine runs, the fuel pump relay is deactivated and comes off.
At this point, the oil pressure-sending unit provides the electricity to the fuel pump. When the ignition is turned off, again, the fuel pump relay is engaged long enough to power down and shut off the fuel pump.
Signs You Have a Faulty Fuel Pump Relay
Before you get out to swap relays and order new stuff, make sure that you can identify any of the signs below first. If you can, then you might want to dig a little deeper into your investigation.
#1. You can’t Start Your Vehicle.
This is by far the most common sign of a faulty fuel pump relay, but it is also the most overlooked sign. People just seem to jump to the conclusion that they either have a dead battery or a bad starter, but if you don’t have gas in the combustion chamber, you will never get it started!
When you turn the key on, you should hear a click in the fuse box, If you don’t hear it and you cannot start your vehicle, you possibly have a bad fuel pump relay.
#2. Check Engine Light (CEL).
If you can get your vehicle started, but it is experiencing mechanical issues, then a check engine light is more than likely your first sign that you are dealing with a faulty fuel pump relay. Luckily for you, there are many engine codes that point you to the fuel pump or fuel pump relay.
Always check the relay first, it will only take a few minutes and could save you hours or a more extensive job.
#3. Engine Stalling.
If your car stalls out after you get it started, it could be a mountain of a problem, but a faulty fuel pump relay is one of the possible issues. Because it is so easy to check, it’s worth ruling out at the beginning of the troubleshooting process.
#4. Rough Acceleration.
If your vehicle’s fuel pump relay has a problem, then you will start to notice some acceleration issues when the fuel pump relay is turned on and off.
That rough acceleration could quickly cause an engine stall, and before you know it, you might not be able to start your vehicle at all!
However, it is worth noting that the fuel pump relay sometimes does not break down slowly. One day, you might have power, and the next day, the vehicle does not start at all.
#5. No Noise from the Fuel Pump.
For you to start your vehicle, you should hear your fuel pump kick on as it sends fuel to the engine. Although there’s a good chance that you will not hear it when you are in the driver’s seat, if someone goes to the back of the vehicle close to the fuel pump, they should hear it kick on.
If they don’t, then you could have an electrical malfunction, a fuel pump that has gone bad, or a fuel pump relay. The fuel pump relay is the cheapest and easiest to fix, so fingers crossed that is the problem!
What makes the Fuel Pump Relay fail?
While technically speaking, a failure of a fuel pump relay due to a short or other electrical malfunction is possible, the vast majority of the time, the problem is just old age!
Each time the relay clicks over, it wears a little bit, and by 100,000, 150,000, or even 200,000 miles, that’s a lot of clicks.
Eventually, that is just too much clicking for it to handle, and it either won’t click over again or it won’t click back to its original position. This is perfection, and as long as it isn’t happening repeatedly, no need to do anything other than replace it.
How to Test a Fuel Pump Relay
Testing a fuel pump relay can be done in three simple ways. The first two methods are not completely foolproof, but they will work 99% of the time and are much easier.
Method 1 – Swap the Relays.
This is the easiest method to check the fuel pump relay. When you pull the fuse box cover off, you will find more than one relay in there. While they serve different purposes, they are all the same.
So, to check any individual relay, simply swap it with another relay! If the problem goes away, it was caused by the relay.
The only downside to this method is that if you have two defective relays, then nothing will change, and you’ll be chasing your tail for a while. That is why it is best to make sure you are swapping in a new relay.
Method 2 – Use a 9-Volt.
Again, this method is still not foolproof, but it catches the problem 99% of the time.
To check a relay with a 9-volt battery, simply remove the relay, connect the positive and negative terminals of the 9-volt battery to the two studs on the relay, and listen for the click.
There is no way to get the terminals on a 9-volt battery wrong, so you shouldn’t need any jumper wires or anything of the sort, and the test is quite quick and simple. If a relay is operating properly, the relay should click over when you connect the battery and click back when you disconnect the battery.
The issue with this test is that relays don’t normally run off 9 volts. Technically, it is close enough to diagnose or troubleshoot just about any relay, but if you are on the edge, what you read could be a false reading. The chances of this happening are slim, but it can happen.
Method 3 – Check Resistance Levels.
Using a multimeter is the only method that is 100% foolproof for checking a relay. Relays operate through resistance.
Once they get enough power, it overcomes the resistance, and the relay clicks over. The actual number of Ohms for your relay can vary somewhat, but should usually be between 50 and 120.
Too few Ohms means your relay is always activated, too many means your relay will not open or will not allow the circuit to close. Your relay will the open or on limit reading that indicates the coil is bad, and you will need to replace it.
Fuel Pump Relay Replacement Cost
If your troubleshooting has led you to a 100% fuel pump relay problem, there is no real reason to have a mechanic assist you. Swapping a relay is quick and easy, and all you typically have to do is purchase the part.
It’s a simple pull the old relay out and push the new one in, that easy! A typical fuel pump relay costs about 25 bucks, which is a very inexpensive part in general.
Just remember, if you go to a mechanic, you may get charged a full hour of labor for a 5-minute job, and that can raise your cost over the $75 threshold depending on the shop’s hourly rate!