Fuel Pump Relay: Why You Should Replace It Sooner

The fuel pump relay is an electromagnetic switch that uses low current to control a higher current circuit. When the fuel pump relay goes bad, the fuel pump won't work properly, leading to issues such as ignition problems, the fuel pump running continuously, and an illuminated check engine light. In some cases, the fuel pump relay may stick closed, causing the fuel pump to run continuously even when the key is out of the ignition. Replacing a fuel pump relay is typically a DIY-friendly repair, with the part costing less than $20. However, it's important to perform a thorough diagnosis to ensure that the issues are specifically due to a faulty fuel pump relay, as other problems can present similar symptoms.

Engine won't start

If your engine won't start, it could be due to a faulty fuel pump relay. The fuel pump relay is an electromagnetic switch that uses low current to control a higher current circuit. When the relay gets enough power, it switches over and sends that power to the fuel pump. When it doesn't, it switches off and the fuel pump shuts down.

• You can't start your vehicle: This is often the most common symptom of a faulty fuel pump relay, but it's also one of the most overlooked. If the combustion chamber doesn't have any fuel, the engine won't start.
• Check Engine Light: If the check engine light is on, there may be a problem with the fuel pump relay. Engine codes can help point you in the right direction.
• Engine Stalling: If your vehicle stalls after starting, it could be due to a faulty fuel pump relay.
• Rough Acceleration: If the fuel pump relay isn't working properly, you may experience acceleration issues. This can eventually lead to engine stalls and an inability to start the vehicle.
• No Noise From the Fuel Pump: When you turn on the vehicle, you should hear the fuel pump kick in. If you don't hear it, there may be an electrical malfunction or a faulty fuel pump or relay.

If you suspect that your fuel pump relay is faulty, there are a few methods you can use to test it:

• Swap the Relays: You can try swapping the fuel pump relay with another relay of the same design in the fuse box. If the problem goes away, then the relay was the issue.
• Use a 9-Volt Battery: Remove the relay and connect the positive and negative terminals of a 9-volt battery to the two studs on the relay. If it's working correctly, you should hear a click when you connect and disconnect the battery.
• Check Resistance Levels: Using a multimeter to check the resistance levels is the only foolproof way to test the relay. If the relay has too few Ohms, it's always activated, and if it has too many, it won't open at all.

If you determine that the fuel pump relay needs to be replaced, it's a fairly simple process:

• Park your vehicle on a flat, hard surface and engage the parking brake.
• Disconnect the negative terminal of the battery to turn off the power to the fuel pump.
• Locate the fuel pump relay in the fuse box, which is usually under the hood or under the dash on the passenger side.
• Remove the fuel pump relay from the fuse box, paying attention to how it comes out so you can insert the new one in the same way.
• Insert the new fuel pump relay into the fuse box.
• Reconnect the negative battery terminal.

By replacing the fuel pump relay, you can hopefully get your engine running again.

Fuel pump runs continuously

If your fuel pump is running continuously, there could be a few reasons why this is happening. Firstly, it is important to note that a fuel pump that runs continuously is not necessarily indicative of a faulty pump. However, if you are experiencing this issue, there are several potential causes and solutions that you can explore.

One potential cause could be a faulty fuel pump relay. The fuel pump relay is responsible for controlling the power supply to the fuel pump, and if it malfunctions, it may cause the pump to run continuously. To diagnose this issue, you can try disconnecting the wire going to the fuel pump relay and checking if the pump shuts off. If the pump continues to run, there may be a short circuit between the relay and the pump. On the other hand, if the pump shuts off, it could indicate a problem with the relay itself or the Powertrain Control Module (PCM).

Another potential cause of a continuously running fuel pump could be incorrect wiring. Ensure that your wiring is connected correctly and that there are no short circuits or damaged wires. Additionally, check for any modifications or "rigging" of the wiring that could be causing the pump to receive constant power.

In some cases, a faulty Powertrain Control Module (PCM) could be the culprit. The PCM controls the fuel pump and injectors, and if it malfunctions, it may cause the pump to run continuously. However, before jumping to this conclusion, it is recommended to check for other potential issues, as a faulty PCM is usually a rare occurrence.

Other potential causes of a continuously running fuel pump could include a faulty oil pressure switch, a bad injector, or a faulty regulator allowing fuel to dump into the intake.

To troubleshoot and resolve the issue, it is recommended to refer to your vehicle's specific repair manual or seek the assistance of a qualified mechanic. They will be able to perform diagnostic tests, inspect the wiring, and recommend the appropriate repairs or replacements.

Check engine light is on

The check engine light turning on is a common symptom of a failing fuel pump relay. The engine control module (ECM) monitors all engine sensors to ensure they are functioning correctly. If the ECM detects any sensor giving an incorrect value, it will turn on the check engine light.

The ECM monitors the fuel pressure with the help of the fuel pressure sensor. If the fuel pump relay suddenly fails, the ECM will turn on the check engine light and store a trouble code relating to the fuel pressure.

The check engine light can also be triggered by a faulty fuel pump, which the fuel pump relay powers. A weakened fuel pump may struggle to provide sufficient fuel pressure during startup, causing extended cranking times or difficulty starting the engine. This can lead to engine performance issues like misfires or stalling, which the vehicle's systems can detect and warn the driver about by turning on the check engine light.

It is important to note that other factors, such as sensor malfunctions or exhaust problems, can also cause the check engine light to illuminate. To distinguish fuel pump issues, pay attention to symptoms like erratic engine performance, misfires, or unusual noises.

If you are experiencing issues with your fuel pump or check engine light, it is recommended to contact a reputable mechanic to diagnose and resolve the problem.

Replacing the relay is a DIY-friendly repair

Part 1: Removing the fuel pump relay

• Turn on the ignition key and listen for the fuel pump to actuate. Also, listen for any buzzing or clicking noise coming from the fuel pump relay.
• Start the engine and check that there is oil pressure. On some vehicles, there will only be an oil light indicator. When the indicator light goes out, there is oil pressure.
• Park your vehicle on a flat, hard surface. Make sure that the transmission is in park for automatics or in first gear for manuals.
• Place wheel chocks around the front tires and engage the parking brake to lock the rear tires from moving.
• Install a nine-volt battery saver into your cigarette lighter to keep your computer live and keep your settings current. If you don't have a nine-volt battery saver, that's okay.
• Open the vehicle's hood and disconnect your battery. Take the ground cable off of the battery's negative post, disabling the power to the fuel pump and sending unit.
• Locate the fuse box in the engine compartment and remove the cover.
• Using the diagram on the fuse box cover, locate the fuel pump relay. You can also refer to your owner's manual for the engine compartment fuse box diagram.
• Remove the fuel pump relay from the fuse box, paying attention to how it comes out so that you can insert the new one in the same way. You may need to use a pair of needle-nose pliers to pull out the fuel pump relay.

Part 2: Installing the new fuel pump relay

• Install the new relay into the fuse box the same way the old relay was removed.
• Put on the fuse box cover and snap it into place. If you removed screws or bolts from the cover, be sure to install them back but do not over-tighten them.
• Remove the fuel cap from the fuel tank and put it back on, ensuring a good seal. This ensures that the fuel system fully pressurizes properly as the fuel pump activates.

Part 3: Checking for fuel pump relay operation

• Reconnect the ground cable back onto the battery's negative post and remove the nine-volt battery saver from the cigarette lighter.
• Tighten the battery clamp and ensure a good connection. If you did not have a nine-volt battery saver, you will have to reset all of the settings in your vehicle.
• Turn the ignition key on and listen for the fuel pump to activate. Turn off the ignition after the fuel pump stops making noise.
• Turn the key on again and listen for the fuel pump relay to buzz or click. You may need an additional person to touch the fuel pump relay to feel the buzz or clicking motion.
• Cycle the ignition key on and off 3 to 4 times to ensure the fuel rail is full of fuel prior to starting the engine.
• Turn the key to start and start up the engine. Monitor how long the start will be engaged for during the cranking period.
• Remove the wheel chocks from the wheels.

Part 4: Test drive the vehicle

• Drive the vehicle around the block. During the test, listen for any unusual noise from the fuel pump or fuel pump relay. Accelerate the engine quickly to make sure that the fuel pump is working correctly.
• Monitor the dashboard for any engine lights. If your engine light comes on after replacing the fuel pump relay, then there may be a need for further diagnosis of the fuel pump assembly or an electrical issue within the fuel system.

By following these steps, you can replace your fuel pump relay at home without needing to take your car to a mechanic.

Relays can be bought online

Future Electronics offers a wide range of relays, including automotive relays, power relays, signal relays, and solid-state relays. They provide relays from industry-leading manufacturers and offer free shipping within the continental US for orders over $50.

Mouser Electronics is another authorized distributor of relays from manufacturers such as IXYS, KEMET, Omron, Panasonic, and Schneider Electric. They stock a large variety of relays, including automotive, general-purpose, high-frequency, and industrial relays.

Additionally, online marketplaces like eBay and Amazon also offer a range of relays from various brands and manufacturers. These platforms often provide customer reviews and ratings, which can be helpful in making an informed purchase decision.

When purchasing a relay online, it is important to carefully review the product specifications and ensure that it is compatible with your specific application. Additionally, consider the reputation of the seller or retailer and read customer reviews to ensure the quality and reliability of the product.

By taking advantage of the convenience of online shopping, you can easily find and purchase the relay you need for your vehicle or project.

Frequently asked questions