Replacing Fuel Pump Relay Switch: Diy Guide

The fuel pump relay is an electromagnetic switch that controls a higher current circuit with low current. It is a vital component for the combustion engine to function, as it ensures the engine gets the fuel it needs to run. When the ignition is turned on, the fuel pump relay supplies a consistent voltage to the fuel pump. A faulty fuel pump relay will cause start-up issues, and in some cases, the engine to stall. To replace the fuel pump relay, you will need to locate the fuse box in the engine bay, which is usually a long black box. Once located, you can remove the fuel pump relay and replace it with a new one.

Locating the fuel pump relay

The relay is featured on a circuit board connected with other fuses and under the command of the car's computer system. If your vehicle has a breakdown or experiences low fuel pressure, the engine light can help you locate the relay to discover and address the issue.

• Check the owner's manual: It often includes a diagram showing the relay's location.
• Look under the hood: Most relays are found in the fuse box under the hood.
• Inspect the fuse box cover: There is usually a diagram that indicates each relay's position.
• Listen for the relay: With the key in the "on" position, you may hear a click from the relay.
• Consult online resources: Many car forums and websites offer specific relay locations for different models.
• Visit a mechanic: When in doubt, a professional can quickly locate and inspect the relay.

Additionally, the fuel pump relay is often a relatively small, rectangular, or square-shaped component with multiple electronic connection pins or terminals. You can also look for a code on the cover of the relay box or search for labels that indicate its purpose, such as 'fuel pump'.

Testing the fuel pump relay

Locate the Fuel Pump Relay:

The fuel pump relay is usually found in the fuse box under the hood or in the passenger compartment. You can refer to your vehicle's owner's manual or a wiring diagram to pinpoint its exact location. The fuel pump relay typically has four or five pins that connect to the wiring harness. To test the relay, you will need to remove it from its socket.

Test the Relay Coil:

The relay coil is responsible for creating a magnetic field when an electric current passes through it. This magnetic field activates the relay switch, allowing power to reach the fuel pump. To test the relay coil, you will need a multimeter and a jumper wire. Set your multimeter to measure resistance (ohms) and connect the jumper wire to the positive battery terminal. Touch one probe of the multimeter to the jumper wire and the other to one of the coil pins on the relay. Repeat this process with the other coil pin. A functional relay coil should give you a reading between 50 and 120 ohms. If the reading is too high, too low, or infinite, the relay coil is defective and requires replacement.

Test the Relay Switch:

The relay switch is responsible for opening and closing the circuit to the fuel pump. To test it, you will again need a multimeter and a jumper wire. Set your multimeter to measure voltage (volts) and connect the jumper wire to the positive battery terminal. Touch one probe of the multimeter to the jumper wire and the other to the pin that connects to the fuel pump. A functional relay switch should display a reading of zero volts. Now, connect the jumper wire to one of the coil pins on the relay and briefly touch the other coil pin with the multimeter probe. You should hear a clicking sound and see a reading of 12 volts on the multimeter. If you don't hear the click or get a different voltage reading, the relay switch is defective and needs to be replaced.

Additional Considerations:

If you encounter issues with your vehicle and suspect a faulty fuel pump relay, it is recommended to first check the FP fuse. A blown fuse could be the culprit and is often a simpler issue to address. Additionally, consult your owner's manual to understand the function of the fuel pump and the potential consequences of a malfunctioning relay.

Replacing the fuel pump relay

The fuel pump relay is an essential component for any combustion engine to function. It is an electromagnetic switch that uses low current to control a higher current circuit. The relay is usually controlled by the ignition or the power control module. When the ignition is turned on, the fuel pump relay supplies a consistent voltage to the fuel pump.

Locating the Fuel Pump Relay

Before you begin to replace the fuel pump relay, you must locate it. The relay can usually be found inside the fuse box in the engine bay, which often looks like a long black box containing various fuses and relays. Depending on the year, make, and model of your vehicle, the fuse box might be located under the hood, in the trunk, near the steering column, or on the firewall. If you are having trouble locating the relay, check your owner's manual for guidance.

Removing the Old Relay

Once you have located the fuel pump relay, carefully remove it from the fuse box. Pay attention to how the relay comes out as the new one will need to go in the same way. You may need to use a pair of needle-nose pliers to help you with this step.

Installing the New Relay

With the old relay removed, you can now install the new fuel pump relay. Ensure that you insert the new relay in the correct way, following the same process as when you removed the old relay.

Testing the New Relay

With the new relay installed, you can now test it to ensure it is working correctly. Turn on the ignition key and wait for the gasoline pump to operate. Listen out for any buzzing or clicking noises coming from the fuel pump relay. If the new relay is working, you should hear these noises.

Post-Replacement Checks

After replacing the fuel pump relay, there are a few additional checks you should carry out:

• Start the engine and check that there is oil pressure.
• Check that the vehicle is parked on a flat, hard surface, with the transmission in park (for automatic transmissions) or first gear (for manual transmissions).
• Ensure that wheel chocks are in place around the tires to prevent the vehicle from moving.
• Disconnect the ground line from the negative post of the battery to turn off the power to the fuel pump.

Cleaning the fuel pump relay

To clean the fuel pump relay, use a blower to remove dust particles. Do not use water, as the relay is an electrical component. Instead, use a small amount of ethanol to thoroughly wipe away any remaining dust or dirt. Allow it to dry for a few seconds before placing it back into the fuse box.

If your fuel pump relay is located in the engine bay, be aware that it can get hot from the engine's heat, which may impede the relay's performance. In addition, dust and dirt can accumulate in the engine bay, so regular cleaning of the relay is recommended.

The fuel pump relay is a cube-shaped object with prongs that connect like an electrical plug. It is usually located in the fuse box in the engine bay but can also be found in other places, such as under the hood, on the firewall, or near the steering column. If you cannot find it, check your owner's manual for the specific location in your vehicle.

Symptoms of a bad fuel pump relay

A faulty fuel pump relay can cause a range of issues with your vehicle, and it is the most common relay to fail. Here are some symptoms of a bad fuel pump relay:

Engine Cranks But Won't Start

The most common sign of a bad fuel pump relay is an engine that cranks but refuses to start. This happens because the fuel pump relay typically fails in the open position, preventing voltage from reaching the fuel pump. As a result, the engine doesn't get the fuel it needs to run.

Fuel Pump Runs Continuously

In rare cases, the fuel pump relay can stick in a closed position, causing the fuel pump to run non-stop. This usually happens in circuits that constantly supply power to the fuel pump fuse. You'll hear the fuel pump running even when the key is out of the ignition.

Illuminated Check Engine Light

In some vehicles, the engine computer or the powertrain control module (PCM) monitors the fuel pump relay and its circuit. If the PCM detects an issue, it turns on the check engine light and stores a corresponding diagnostic trouble code (DTC) in its memory. However, not all vehicles will turn on the check engine light for a bad fuel pump relay.

Multiple Failed Start Attempts

You may experience multiple failed attempts to start your vehicle, especially when the engine is cold in the morning. This problem tends to get worse over time, eventually leading to a complete failure to start the engine.

Unexplained Battery Drainage

A fuel pump relay that is stuck in the closed/on position can cause unexplained battery drainage. You may be able to hear the fuel pump running from the rear of the vehicle even after it has been turned off. Battery drainage may persist even after installing a new battery or fuel pump.

Jump Starting Resolves Starting Issues

Jump-starting your vehicle may temporarily fix your starting issues as fuel pump relays perform better at higher voltages. When using a jump start from another running vehicle, the alternator outputs a higher voltage, improving the performance of the fuel pump relay.

Seasonal Starting Issues

Your vehicle may start without issues during the warmer months but struggle to start during the colder months.

Stalling After Starting or While Driving

Your vehicle may start but stall shortly after, or it may stall while driving, causing you to coast to a stop. While this issue is occasionally related to a faulty fuel pump relay, it is more likely due to a thermal expansion problem inside the TIPM or other electrical components.

Frequently asked questions