Replacing Fuel Pump Relay: Diy Guide To Fixing Your Car

The fuel pump relay is an electromagnetic switch that helps your vehicle start by pressurising the fuel system for the first few seconds before the oil pressure takes over. The relay is usually located in the vehicle's long black box with the other relays and fuses, but this can differ between cars. A failing fuel pump relay can cause ignition issues, the fuel pump running continuously, and an illuminated check engine light. To replace a fuel pump relay, you will need to disconnect the battery, locate the fuse box, remove the old relay, install a new one, and then re-pressurise the fuel system.

Locating the fuel pump relay

The fuse box is usually found underneath the hood near the front of the vehicle, but there may also be a smaller fuse box under the steering column inside the car. The fuel pump relay is typically coloured green or grey, and there may be a diagram on the inside of the fuse box cover to help you locate it. If you are still unable to find it, check your vehicle's manual.

Once you have located the relay, you can then proceed to test or replace it.

Disconnecting the battery

Step 1: Park Your Vehicle Safely

Before beginning any work on your vehicle, it is important to ensure it is securely parked. Find a flat, hard surface and make sure the vehicle is in park (for automatics) or in first gear (for manuals). Engage the parking brake to prevent any accidental movement. If you are working on a slope or uneven surface, you may also want to place wheel chocks around the tires for added safety.

Step 2: Prepare for Battery Disconnection

Open the hood of your vehicle to access the engine compartment. At this stage, it is recommended to install a nine-volt battery saver into your cigarette lighter. This handy device will keep your computer live and maintain your current settings. However, if you do not have one, it is not essential, and you can proceed without it.

Step 3: Locate the Battery

The battery is usually located in the engine compartment and is typically clearly visible. It is a large, rectangular unit with two terminals: a positive (+) and a negative (-). These terminals will have cables attached to them, which provide power to various electrical components in your vehicle.

Step 4: Disconnect the Negative Cable

To disconnect the battery, you will need to remove the cable from the negative terminal. Use a wrench or a pair of pliers to loosen the nut or bolt holding the cable in place. Once it is loose, carefully lift the cable off the terminal. Be cautious not to let the cable touch any metal parts of the vehicle, as this could cause a short circuit. You may cover the terminal with tape or a protective cap for added safety.

Step 5: Disconnect the Positive Cable (Optional)

While disconnecting the negative cable is sufficient to shut off the power, you may also choose to disconnect the positive cable for added precaution. Follow the same procedure as for the negative cable. Remove the cable from the positive terminal, ensuring it does not come into contact with any metal parts.

At this point, both the positive and negative terminals should be free of cables, and the battery is now disconnected. You can proceed with changing the fuel pump relay, following the steps provided in other sources. Remember to reconnect the battery cables in the correct order and tighten the connections securely before starting your vehicle.

Removing the old relay

To remove the old fuel pump relay, you will need to locate it first. The fuel pump relay is usually located in the vehicle's long black box with the other relays and fuses, often in the engine bay. However, the location can differ between cars, so if you cannot find it, check your owner's manual.

Once you have located the fuse box, you will need to remove its cover. Some fuse boxes are held on with hex screws or bolts and require a ratchet to remove them, while others are held on with clips. With the cover removed, you can now refer to the diagram on the fuse box cover to locate the fuel pump relay. If there is no diagram, consult your owner's manual for the engine compartment fuse box diagram.

When you have identified the fuel pump relay, it's time to remove it. Pay attention to how the relay comes out, as the new one will need to go in the same way. In some cases, you may need to use a pair of needle-nose pliers to pull out the relay. If the relay is within the box, carefully pry it out with a flathead screwdriver.

Now that you have removed the old fuel pump relay, you can take it to an auto supply store to get the correct replacement.

Installing the new relay

Now that you've identified the problem and removed the old fuel pump relay, it's time to install the new one. Here's a detailed guide on how to do it:

Before you begin, ensure you have the correct replacement relay. You can use the old relay as a guide to get the right one. The new relay should fit into the fuse box the same way the old one was removed.

Step 1: Install the new relay into the fuse box. Ensure it's positioned correctly and securely in place.

Step 2: Put the cover back on the fuse box. Snap it into place or use screws or bolts if necessary. Be careful not to over-tighten the screws to avoid stripping them.

Step 3: Repressurize the fuel system. This is important because the system loses pressure when you remove the old relay. Ensure the gas cap is secure, then turn the ignition on for about 2 seconds and shut it off for up to 10 seconds. Repeat this process at least 5 times, or as recommended for your specific vehicle.

Step 4: Reconnect the battery cables. Reconnect the ground cable to the negative terminal of the battery. If you disconnected the positive terminal as well, reconnect it now. Ensure the connections are tight and secure.

Step 5: Test the new relay. Turn the ignition key on and listen for the fuel pump to activate. You may need to cycle the ignition key on and off a few times to ensure the fuel rail is full before starting the engine.

Step 6: Start the engine and monitor its performance. Observe how long the engine takes to start and listen for any unusual noises from the fuel pump or relay.

Step 7: Test drive the vehicle. Drive the car around the block and listen for any unusual noises. Accelerate the engine to ensure the fuel pump is functioning correctly.

Step 8: Check for any warning lights on the dashboard. If the engine light comes on, further diagnosis or professional assistance may be required.

It's important to follow these steps carefully to ensure the new fuel pump relay is installed correctly and functioning properly. If you encounter any issues or complications, it's recommended to consult a certified mechanic for assistance.

Repressurising the fuel system

Step 1: Secure the Gas Cap

Firstly, ensure that the gas cap on your vehicle is securely tightened. This step is crucial as a loose gas cap can lead to fuel vapour leaks and affect the overall pressure in the fuel system.

Step 2: Turn the Ignition On and Off in Intervals

Once the gas cap is secure, you can proceed to turn the ignition on for approximately two seconds and then shut it off for about five to ten seconds. This process should be repeated at least three to five times, depending on your vehicle's specific requirements. During this process, you may hear the fuel pump buzzing for a couple of seconds before it automatically shuts off. This safety feature ensures that the fuel pump doesn't run continuously if the car isn't started.

Step 3: Attempt to Start the Vehicle

After completing the ignition cycle, you can now try to start your car. The fuel system should now be adequately repressurised, allowing the engine to receive the required fuel pressure for a successful start.

Additional Notes

It is important to note that the procedure for repressurising the fuel system may vary slightly depending on the year, make, and model of your car. Modern fuel-injected vehicles typically have higher fuel pressure, ranging from 32 to 60 pounds, compared to older carbureted systems. Additionally, if you are working on a carbureted system with a manual fuel pump, the standard procedure may not apply. In such cases, you may need to crank the engine a few times to fill the fuel bowls before attempting to start the vehicle.

Frequently asked questions