Replacing Fuel Pump Relay: Step-By-Step Guide For Your Car

A fuel pump relay is an electromagnetic switch that uses low current to control a higher current circuit. It is a necessary component for the combustion engine model to function, ensuring the engine gets the fuel it needs to run. The relay is usually located in the vehicle's long black box with the other relays and fuses, but this can differ between car models. Replacing a fuel pump relay is a relatively simple task, and a new relay can be purchased for between $12 to $45.

How to identify a faulty fuel pump relay

A faulty fuel pump relay can manifest in several ways, and it is important to identify the issue to ensure optimal vehicle performance and longevity. Here are some common signs of a failing fuel pump relay:

Engine Cranks But Doesn't Start

The most common sign of a faulty fuel pump relay is an engine that cranks but refuses to start. This usually happens when the relay fails in the open position, preventing voltage from reaching the fuel pump. As a result, the engine doesn't receive the required fuel and won't run.

Intermittent Starting Issues

The fuel pump relay may malfunction intermittently, leading to sporadic starting problems. Your vehicle might start without issues on some occasions, but you may experience delayed or difficult starts at other times.

Engine Stalling

A faulty fuel pump relay can cause the engine to stall or shut off unexpectedly. This is often due to a sudden loss of power to the fuel pump, resulting in insufficient fuel or pressure in the combustion chamber.

No Sound from Fuel Pump

When you turn on the ignition, the fuel pump should make a whirring sound as it increases the fuel pressure in the rail. If you don't hear this sound, it could be a sign that the fuel pump relay is malfunctioning.

Fuel Pump Runs Continuously

In rare cases, the fuel pump relay can get stuck in the closed position, causing the fuel pump to run continuously, even when the key is out of the ignition. This issue can lead to unnecessary battery drain.

Check Engine Light Illuminated

A malfunctioning fuel pump relay can trigger the Check Engine Light on your dashboard. This warning light indicates a disruption in the fuel delivery system, and you may also notice relevant diagnostic trouble codes (DTCs).

Difficult Acceleration

A faulty fuel pump relay can reduce the power to the fuel pump, leading to a decrease in fuel delivery to the engine. This can result in difficulties with acceleration and overall engine performance.

Engine Misfires or Hesitation

Insufficient fuel pressure due to a faulty fuel pump relay can cause engine misfires, hesitation, or a lack of power during acceleration. Inadequate fuel supply affects the combustion process, leading to these performance issues.

Noisy Fuel Pump Operation

A failing fuel pump relay may cause the fuel pump to operate noisily, producing unusual buzzing, whining, or clicking sounds. This indicates that the fuel pump is struggling to receive the proper power.

Engine is Fully Dead

A malfunctioning fuel pump relay can leave the engine completely dead and unable to start. If the fuel pump relay fails, there will be no power to the fuel pump, resulting in a lack of fuel pressure to start the engine.

Inconsistent Fuel Pressure

A malfunctioning fuel pump relay can cause irregularities in the fuel pump's operation, leading to inconsistent fuel pressure. This can affect the engine's performance and fuel efficiency.

If you notice any of these symptoms, it is recommended to consult a qualified mechanic or refer to your vehicle's owner's manual for further guidance on diagnosing and addressing fuel pump relay issues.

Locating the fuel pump relay

The fuse box is usually located either under the dashboard or under the hood, near the battery. Once you have found the fuse box, look for a diagram that shows the location of the relays. The diagram should indicate where the fuel pump relay is in relation to the other relays in the box. If there is no diagram, you can check online for your specific model.

The fuel pump relay is usually coloured green or grey, and it connects to the vehicle's electrical system, so make sure the vehicle is turned off before attempting to remove it.

If you are still unable to locate the fuel pump relay, you can refer to your vehicle's manual, which should list its location.

Removing the fuel pump relay

The fuel pump relay is usually located in the vehicle's long black box with the other relays and fuses, which is often the fuse box in the engine compartment. However, the location can differ between cars, so if you can't find it, check your owner's manual.

Before you begin, park your vehicle on a flat, hard surface, with the transmission in park (for automatics) or in 1st gear (for manuals). Place wheel chocks around the front tires and engage the parking brake to prevent the vehicle from moving.

Now, follow these steps to remove the fuel pump relay:

• Install a nine-volt battery saver into your cigarette lighter to keep your computer live and your settings current.
• Disconnect your battery. Take the ground cable off the battery's negative post to disable the power to the fuel pump and sending unit. Disconnecting the positive terminal is also recommended as a precaution.
• Open the vehicle's hood and locate the fuse box in the engine compartment.
• Remove the cover from the fuse box. Note that 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.
• Using the diagram on the fuse box cover, locate the fuel pump relay. This is usually a cube-shaped object that connects with prongs like an electrical plug. If there is no diagram, 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 as the new one will need to be inserted the same way. You may need to use a pair of needle-nose pliers to pull it out.
• Once removed, inspect the relay for any signs of corrosion or overheating.

Installing a new fuel pump relay

Step 1: Purchase the Correct Relay

Before installing a new fuel pump relay, it is important to purchase the correct replacement. Take the old relay to an auto supply store and use it as a guide to find the correct replacement. The price of a new relay can range from $12 to $45, and some brands may be more reliable than others. Consult a store specialist to find the best relay brand for your vehicle.

Step 2: Install the New Relay

Locate the fuse box in the engine compartment, which is usually a long black box containing various relays and fuses. Place the new relay into the fuse box in the same way the old relay was removed. Ensure that the new relay is secure and properly connected.

Step 3: Re-connect the Battery

Reconnect the ground cable back onto the negative post of the battery. If you did not use a nine-volt battery saver, you will need to reset all the settings in your vehicle, such as the radio, electric seats, and mirrors. Tighten the battery clamp to ensure a good connection.

Step 4: Repressurize the Fuel System

To do this, ensure the gas cap is secure, then turn the ignition on for 2 seconds and shut it off for up to 10 seconds. Repeat this process at least 5 times, depending on your vehicle's recommendations.

Step 5: Test the Fuel Pump Relay

Turn the ignition key on and listen for the fuel pump to activate. Turn off the ignition after the fuel pump stops making noise, then turn it on again to 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 vibration. Cycle the ignition key on and off 3 to 4 times to ensure the fuel rail is full of fuel before starting the engine.

Step 6: Start the Engine and Test Drive

Turn the key to start and start up the engine. Monitor the engine's performance and listen for any unusual noises from the fuel pump or fuel pump relay. During the test drive, accelerate the engine quickly to ensure the fuel pump is working correctly. Monitor the dashboard for any engine lights, which may indicate further issues.

If you encounter any problems during the installation process or if the engine light comes on after replacing the fuel pump relay, seek assistance from a certified technician to inspect the fuel pump relay and diagnose the problem.

Repressurising the fuel system

Firstly, ensure that the gas cap is securely fastened. This is an important precaution to prevent any fuel leakage during the repressurisation process. Once the gas cap is secure, you can proceed to the next step.

Now, you will need to turn the ignition on for approximately two seconds, and then shut it off for up to ten seconds. This sequence is essential to building up pressure in the fuel system. Repeat this cycle at least five times. However, it is important to note that the recommended number of repetitions may vary depending on the vehicle. Refer to your vehicle's manual or consult a mechanic for specific instructions for your car model.

After completing the pressurisation cycles, you can proceed to test the fuel pump relay. This can be done by swapping the fuel pump relay with a similar one in the fuse box, such as the air conditioner relay. If the car starts with the second relay connected, it confirms that the original fuel pump relay was faulty and required replacement.

It is important to note that repressurising the fuel system is a crucial step when changing the fuel pump relay. This process ensures that the fuel system is functioning optimally and safely. Always exercise caution when working with fuel systems and refer to a professional mechanic if you have any doubts or concerns.

Frequently asked questions