Modern automotive engines are designed to use a precise amount of fuel at any given moment. The fuel pump relay is responsible for this.
So if you are to get the most automotive experience from your car, you need to recognize the common signs and symptoms of bad fuel pump relay.
The fuel pump relay is responsible for powering the fuel pump so that the precise amount of fuel is delivered to the injectors and, ultimately, the combustion chamber. It is a device that contains electrical components fitted into a small aluminum or plastic cylinder box.
It comes in different ratings and dimensions and is situated in different locations in the vehicle (depending on the brand and model).
Going by the role of the fuel pump relay, we are going to discuss the symptoms of a bad fuel pump relay and how to fix it.
What is a Fuel Pump Relay?
The fuel pump relay is a necessary component for the combustion engine model to function.
The combustion engine needs fuel to run, and this component ensures that that engine gets what it needs. It is usually controlled by the ignition or the power control module.
When you turn on the ignition, it is activated and will supply electricity to turn on the fuel pump. When you shut off the ignition, it powers down the fuel pump.
What Does a Fuel Pump Relay Do?
A relay is basically an electromagnetic switch that uses low current to control a higher current circuit. Inside the relay, you’ll find a coil and a switching mechanism with a set of contacts.
Most automotive relays are normally open, meaning current does not flow between the contacts until the relay is activated.
In a typical automotive fuel pump circuit, a control module activates the relay. When the module deems conditions are correct, it supplies ground to the coil inside the relay, causing current to flow through the coil.
The current flowing through the coil creates a magnetic field that pulls the relay’s contacts closed. Current then travels across the contacts to the electric fuel pump, causing the pump to turn on.
Once activated, the electric fuel pump moves fuel from the fuel tank to the fuel injectors in the engine. The injectors supply the fuel needed to make the engine run.
Where is the Fuel Pump Relay Located?
In most car types, the fuse box under the dashboard or the fuse box in the engine compartment houses the fuel pump relay.
A lengthy, black box with multiple fuses and relays, including one for the fuel pump, is typically the fuse box for the engine or dashboard. For different autos, the fuel pump relays could be mounted in different places.
Consult your vehicle’s owner’s manual to identify the fuel pump relay’s precise placement quickly.
Symptoms of Bad Fuel Pump Relay
The most common symptoms of a bad fuel pump relay are a stalling engine, performance issues, and a check engine light on your dashboard.
If your car won’t start at all and you can’t hear the fuel pump when you turn on the ignition, it could also be due to a bad fuel pump relay.
The relay can fail for many reasons, from dust to electrical power surges; anything can affect the well-being of a fuel pump relay.
Here is a more detailed list of the signs of a bad or failing fuel pump relay to look for:
#1. Check Engine Light on.
The engine control module monitors all engine sensors to ensure they do not show the wrong values.
If the ECU suspects any sensor is giving an incorrect value, it will light up the check engine light. A check engine light is also the most common sign of a bad fuel pump relay.
The ECU monitors the fuel pressure with the help of the fuel pressure sensor. If the fuel pump relay suddenly fails, it will light up the check engine light and store a trouble code relating to the fuel pressure.
#2. Rough Acceleration.
The fuel pump relay going bad can affect the fuel pump’s power and affect fuel delivery to the engine. An engine runs on fuel just like the heart of a human runs on oxygen and blood.
Therefore, any fuel pump relay issues will affect fuel flow to the combustion chamber, and your vehicle might have problems starting.
However, this can happen due to several other reasons, such as a choked fuel filter, so you should always properly diagnose your car before replacing any parts.
#3. Engine Stalling.
If the fuel pump relay has any bad soldering’s inside it, it might suddenly lose the relay connection and stop delivering power to the fuel pump.
The engine turns off if the combustion chamber’s fuel is inadequate or doesn’t have the proper pressure.
The part that ensures none of this happens is the fuel pump, and it cannot work perfectly if the fuel pump relay develops any issues.
#4. Engine is completely dead.
A faulty fuel pump relay can also cause the engine not to start at all and be completely dead. No fuel pressure means that your engine will never start, and if the fuel pump relay has failed, it will not give any power to the fuel pump to build up fuel pressure.
#5. No noise from the fuel pump on ignition.
When you turn the ignition on in the ignition lock, you should hear a whirring noise from the rear of the car. This means that the fuel pump started building fuel pressure in the fuel rail.
If you can’t hear this, there might be a problem with the fuel pump relay. You can try to listen closely to the fuel tank for any noise for 2-3 seconds after turning the ignition on.
What Causes a Fuel Pump Relay to Go Bad?
Most fuel pump relays fail from heat, age, wiring issues, or overload from a worn fuel pump.
#1. Heat, Vibration, and Age-Related Wear.
Heat and vibration slowly break down the relay’s internal parts. Over time, solder joints can crack. Contacts can burn or pit from normal use. Each time the relay clicks, a small spark forms. After thousands of cycles, that wear adds up.
When contacts burn, they may stick or fail to pass enough current. That’s when you see random stalls or no-start events. These problems often happen when the engine bay is hot.
#2. Electrical Issues (Poor Connections, Corrosion, Moisture).
Moisture and corrosion in the fuse box can shorten a relay’s life. If water gets into the box, relay pins can rust. A loose terminal can cause arcing and heat. Corrosion adds resistance. This makes the relay run hotter and fail sooner.
In areas with road salt or heavy rain, you might see green or white crust on pins. Any time you pull a relay, check for this. Clean or repair the socket if needed.
#3. Overloaded Circuits or Shorted Fuel Pumps.
A dragging or shorted fuel pump can overload the relay and burn it out. If the pump draws too much current, the relay handles more heat than it should. Over time, that heat can melt plastic. It can warp contacts or weld them shut.
That’s why a good shop checks both the relay and the pump. Replacing the relay without fixing a failing pump can lead to another relay failure later.
How to Diagnose a Bad Fuel Pump Relay (Step-by-Step)
The best way to diagnose a bad fuel pump relay is to listen for the pump, check fuses and the relay, then test power and scan for codes.
Step 1: Listen for the Fuel Pump on Key-On.
Listening for the pump priming is your fastest first check. Sit in a quiet spot. Turn the key to “ON” without cranking. Listen near the back seat or fuel filler. You should hear a 2–3 second hum.
If you don’t hear anything, you may have a relay, fuse, wiring, or pump problem. This simple step tells you the pump isn’t getting power at key-on.
Step 2: Locate the Fuel Pump Relay and Check Fuses.
Finding the relay and checking the fuses comes next. Use your owner’s manual or fuse box diagram to find the pump fuse and relay. Pull the fuse and see if it’s blown. Inspect the relay and socket for heat damage, burning, or corrosion.
If a fuse is blown, replace it once. If it blows again, you may have a shorted pump or wiring. Don’t keep putting in new fuses. That can cause more damage.
Step 3: Swap the Relay with a Matching One (Easy “Horn Test”).
Swapping a relay with a twin part is a quick real-world test. Many fuse boxes use the same size relay for things like the horn, A/C, or fan. If another relay has the same part number, swap it with the fuel pump relay. Then try to start the car.
If the car starts after the swap, and the horn stops working, you likely found a bad relay. Swap them back after the test and replace the bad one. This trick is simple and needs no tools.
Step 4: Test with a Test Light or Multimeter.
A test light or multimeter can confirm power and ground at the relay. With the relay removed, use a wiring diagram to find the power, ground, and control pins.
Check for battery voltage at the feed pin. Check for a good ground. Then check if the control side gets power when you turn the key.
You can also measure resistance across the relay’s coil. Check continuity across the switched pins when you energize it. If the coil is open or the contacts never close, the relay is bad.
Step 5: Scan for Codes and, If Needed, Check Fuel Pressure.
Scanning for codes and checking fuel pressure show you the bigger picture. Use an OBD2 scanner to look for pump circuit or low pressure codes.
The Car Buzz has a full guide on how to use an OBD2 scanner. We also help you pick a good car code reader if you don’t have one.
If the relay tests good but you still have no start or stalls, a fuel pressure test can confirm if the pump itself is failing. Many parts stores loan pressure gauges if you want to test at home.
How Do You Test A Fuel Pump Relay?
Materials needed:
- Multimeter.
- Wiring diagram for the specific vehicle model and year.
- Battery terminal tool or 10mm wrench.
- 12V power supply.
It is pretty simple to do that. Follow these steps:
Step 1: Park the car on safe and level ground.
Engage the vehicle’s parking brake and put the transmission in “Neutral” or “Park.
Step 2: Turn the ignition key in the “ON” position.
After doing this, try to listen hard for the sound of the fuel pump, this is often a faint buzzing or clicking sound that might escape your notice if you don’t pay attention. Do not be bothered if you don’t hear any sounds.
Step 3: Locate the fuel pump relay.
For most cars, the fuel pump relay is situated in the engine compartment. The internet, the owner’s manual, or the service manual all of these are great go-to resources for locating the relay. You might even find a fuel pump relay diagram while searching for the location.
Once you have located the relay, try to pay closer attention to it to listen to the clicking or buzzing sound while the key is still in the “ON” position. You might get someone to join you at this point.
Step 4: Disconnect the negative cable from the car battery.
The idea is to disable the power that is sent to the fuel pump and the related circuits. A wrench or socket set should make this task easier for you.
Step 5: Remove the fuel pump relay.
You can do this using a pair of needle-nose pliers if you find it difficult to do with your bare hands.
Step 6: Set Your Multi-meter tool to resistance mode.
At this point, you should connect test lights (preferably multi-meter) to the load and battery pins in the fuel pump relay. Connect the ground of the power supply to the ground pin in the relay.
Step 7: Send power to the input voltage pin.
The multi-meter tool should make a beeping sound every time you do this. If that does not happen, your fuel pump relay is either broken or burned out.
Testing your fuel pump relay should be the next step after you have noticed any of the symptoms described above. Here is a video on how to test a fuel pump relay. It should make the troubleshooting process easier for you.
Fuel Pump Relay Replacement Cost
The average fuel pump replacement cost is between $90 and $150, depending on the car model and labor costs. The parts may cost you between $20 and $50, while the remaining cost is labor.
The fuel pump relay is a small electronic device easily acquired online or at the nearest spare parts shop. The fuel pump relay’s replacement cost involves the cost of the parts and the labor cost that the mechanic would charge you.
When considering the labor cost, it could be at least an hour of work or more in certain cases.
The amount the repair shop charges you will depend on your mechanic’s hourly pay rate or the per-hour cost. Other than the labor cost, the fuel pump relay is not a very expensive device, and you can buy one for $20 to $50 on average for most vehicles.
FAQs.
Q: Will A Car Run With A Bad Fuel Pump Relay?
That depends on the extent of damage to the fuel pump relay. Once there is an issue with your fuel pump relay, the fuel supply to your vehicle’s engine gets cut off, and the engine loses power and stalls.
If the fault in the fuel pump relay is minimal, the vehicle might be able to start after a while. On the flip side, your car will not start if the fuel pump relay is completely damaged. So can a fuel pump relay work intermittently? It depends on the extent of damage to the relay.
Q: Can I Bypass the Fuel Pump Relay?
You could bypass a fuel pump relay by using a jumper assembly that comes with a toggle switch that you can use to turn the fuel pump on and off manually.
Here is something you should know. It is okay to bypass your fuel pump relay if it is something of a test for the wiring or the relay.
However, if your fuel pump works after you must have bypassed the fuel pump relay, the relay is most likely bad. It is a bad idea to try to drive around with a vehicle that has a jumped fuel pump relay.
That said, a fuel pump relay bypass offers a way on how to start a car with a bad fuel pump relay.
Final Words
It is essential to know and recognize the common signs and symptoms of a bad fuel pump relay, and how to fix it to prevent further damages that could result from it.
Why? Because y our vehicle’s fuel pump relay is a vital component that prompts your fuel pump to start once you fire your engine. It is prone to wear and tear that could cause it to get damaged like all devices.
Once the fuel pump relay goes bad, the fuel supply to the engine is cut off, and your engine stalls. We have described some of them in this article, so hopefully, you can avoid the complications of a bad fuel pump relay like engine misfire.