Fuel Pump Relay: When To Know It's Time For A Change

The 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 to function, as it ensures the engine gets the fuel it needs to run. The relay is usually controlled by the ignition or the power control module and can be found in the fuse box in the engine bay.

The fuel pump relay can fail in two ways: it can fail to open, causing the fuel pump to run continuously, or it can fail to close, preventing voltage from reaching the fuel pump and causing the engine to be starved of fuel and refuse to start.

Some common symptoms of a failing fuel pump relay include ignition issues, the fuel pump running continuously, and an illuminated check engine light. If you suspect your fuel pump relay has failed, you can test it by temporarily swapping it with another relay from the power distribution box. If your fuel pump runs with the alternate relay installed, you know the fuel pump relay needs to be replaced.

No humming sound when ignition is turned on

If you don't hear the fuel pump humming when you turn on the ignition, it could be a sign that something is wrong with the fuel pump relay. The fuel pump relay is an electromagnetic switch that uses low current to control a higher current circuit. When the ignition is turned on, the fuel pump should prime the fuel system by creating a buzzing or humming sound for 1-2 seconds. This sound indicates that the fuel pump is working properly. However, if there is no humming sound, it could be due to a faulty fuel pump relay.

There are a few things you can check if you don't hear the fuel pump humming:

• Check the fuel pump fuse: A blown fuse could be the reason why the fuel pump is not working. Try replacing the fuse and see if that restores the humming sound.
• Test for power: Use a multimeter to test for power at the fuse pin cavities. This will help determine if there is an issue with the power supply to the fuel pump.
• Check the oil pressure sending unit: In some vehicles, the fuel pump is tied to the oil pressure sending unit. If the sending unit goes bad, it can shut down the fuel pump, resulting in no humming sound.
• Check for trouble codes: Connect a code reader or scan tool to the vehicle's diagnostic port to check for any trouble codes that may be related to the fuel pump or engine computer. This can help identify if there are any issues with the fuel pump relay or other components.
• Test the fuel pump relay: Try temporarily swapping the fuel pump relay with another relay of the same design from the power distribution box. If the fuel pump runs with the alternate relay, it confirms that the original fuel pump relay is faulty and needs replacement.

It is important to note that other issues could also cause the absence of a humming sound when the ignition is turned on. Therefore, it is recommended to perform a thorough diagnosis of the vehicle before replacing any parts.

Car cranks for longer than usual

If your car cranks for longer than usual, there could be a few reasons why. Here are some possible causes and troubleshooting tips:

Possible Causes

• A faulty fuel pump relay: The fuel pump relay is an electromagnetic switch that controls the fuel pump's power. If it fails, the engine won't get enough fuel and won't start.
• A faulty fuel pump: If the fuel pump itself is faulty, it won't be able to deliver fuel to the engine, resulting in a no-start condition.
• Air in the fuel system: If your vehicle has run out of fuel or you've recently replaced fuel system components, air may be trapped in the system, preventing the engine from starting.
• Wrong type of fuel: Using the wrong type of fuel, such as diesel in a gasoline engine or vice versa, will cause the engine to crank but not start.
• Old or contaminated fuel: If your car has been sitting for a long time, the fuel may have degraded or become contaminated, affecting the engine's ability to start.

Troubleshooting

• Check for fuel pump relay issues: Locate the fuel pump relay in the fuse box and refer to your owner's manual for specific testing procedures. You can try swapping it with another relay or using a multimeter to check for continuity.
• Verify fuel pump operation: Ensure that the fuel pump is receiving power and functioning properly. Listen for any unusual noises during cranking, indicating possible fuel pump issues.
• Check for correct fuel type: Confirm that you are using the correct type of fuel for your vehicle (gasoline or diesel).
• Drain and refill the fuel tank: If you suspect old or contaminated fuel, drain the fuel tank and refill it with fresh, clean fuel.
• Purge air from the fuel system: If air is trapped in the fuel system, you may need to crack the injectors or seek professional help to purge the air and restore proper fuel delivery.

If you've checked these potential issues and your car still cranks longer than usual, it's advisable to consult a professional mechanic for further diagnosis and repair.

Illuminated check engine light

An illuminated check engine light is one of the most common signs of a bad fuel pump relay. When the fuel pump relay goes bad, the engine computer, also known as the powertrain control module (PCM), may detect a problem and turn on the check engine light. This light indicates a fuel system problem that requires attention.

On certain vehicles, a bad fuel pump relay can cause a diagnostic trouble code (DTC) to be stored in the PCM's memory. Code P0230 "Fuel Pump Primary Circuit" is one such code, but it's important to note that not all vehicles will support this code. As a result, the check engine light may not illuminate for a bad fuel pump relay in some cases.

It is important to perform a thorough diagnosis of the vehicle before replacing any parts, as other issues can present similar symptoms. In addition to checking the fuel pump relay, you should also check the fuel pressure, listen for unusual noises from the fuel pump, and inspect the fuel pump relay circuit.

A temporary solution to a bad fuel pump relay is to swap it with a similar relay in the vehicle's relay box. However, this is only a quick fix, and it is recommended to replace the fuel pump relay or the fuel pump itself for a permanent solution.

Engine doesn't start

If your engine cranks but doesn't start, it could be a sign of a bad fuel pump relay. This is the most common symptom of a failing fuel pump relay. The fuel pump relay will likely fail in the open position, preventing voltage from reaching the fuel pump. As a result, the engine will not receive the fuel it needs to run.

Before replacing the fuel pump relay, it's important to perform a thorough diagnosis of the vehicle as other problems can cause similar symptoms.

To test the fuel pump relay, you can try swapping it with another relay from the power distribution box, such as the air conditioning compressor relay. If the fuel pump runs with the alternate relay installed, the fuel pump relay needs to be replaced.

You can also test the fuel pump relay using a multimeter or by following the process outlined in many online videos.

The fuel pump relay is typically located in the power distribution box in the engine compartment. You can consult your owner's manual or the diagram on the fuse box cover to locate it.

If you need to replace the fuel pump relay, it is a relatively inexpensive repair that you can often do yourself. The part itself usually costs less than $20, but the cost can vary depending on the vehicle's make, model, and year.

In addition to an engine that cranks but doesn't start, other symptoms of a bad fuel pump relay include the fuel pump running continuously and an illuminated check engine light.

Testing the Fuel Pump Relay

To test the fuel pump relay, make sure you have the following tools:

• Needle-nose pliers
• Ratchet with metric and standard sockets
• Wheel chocks
• Nine-volt battery saver (optional)

• Turn on the ignition key and listen for the gasoline pump to operate. You may also hear a buzzing or clicking noise coming from the fuel pump relay.
• Start the engine and check the oil pressure. Look for an oil light, which may be the only signal on some vehicles. The light turning off indicates that there is oil pressure.
• Park your vehicle on a flat, hard surface and engage the parking brake.
• Place wheel chocks around the front tires if you are parking on a slope.
• Install a nine-volt battery saver into the cigarette lighter to keep your computer activated and vehicle settings current (optional).
• Open the vehicle's hood and disconnect the battery. Remove the ground line from the negative post of the battery to turn off the power to the fuel pump.
• Locate the fuel pump relay using the diagram on the fuse box cover or your owner's manual.
• 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. You may need to use needle-nose pliers to pull it out.
• Test the fuel pump relay using a multimeter or by swapping it with another relay, as mentioned earlier.
• If the fuel pump relay is bad, replace it with a new one, ensuring it is inserted correctly.

A bad fuel pump relay can cause issues with your engine starting. By performing a thorough diagnosis and following the testing procedure outlined above, you can identify and replace a faulty fuel pump relay. It is important to address this issue promptly to avoid more expensive repairs down the line.

No noise from the fuel pump

If there is no noise coming from the fuel pump, 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 ignition key is turned on, the fuel pump should operate, and a buzzing or clicking noise should be heard from the fuel pump relay. If there is no noise, it could indicate a problem with the relay.

To diagnose a faulty fuel pump relay, you can start by turning on the ignition key and listening for any noise from the fuel pump relay. If there is no noise, you can then check the fuse box to locate the fuel pump relay. The relay is typically located in the power distribution box in the engine compartment. You can refer to your vehicle's owner's manual to identify the correct relay. Once located, you can remove the relay from the fuse box and inspect it for any signs of damage or corrosion.

If the fuel pump relay appears to be damaged or corroded, it should be replaced. The cost of a fuel pump relay is usually less than $20, and it is a DIY-friendly repair that can be done at home. However, it is important to note that other issues could also cause a lack of noise from the fuel pump, such as a faulty fuel pump or a problem with the wiring.

To further diagnose the issue, you can perform a continuity test on the fuel pump relay using a multimeter. Additionally, checking the voltage at the fuel pump terminals can help determine if the issue is with the relay or the pump itself. If there is no voltage at the terminals, the problem is likely with the relay or the wiring. If there is voltage, but the pump is not running, the pump may be faulty and may need to be replaced.

In some cases, the fuel pump may not produce any noise even when it is functioning correctly. This could be due to a weak or failing fuel pump, which may still be delivering fuel to the engine but at a lower pressure or flow rate. Therefore, it is important to perform comprehensive diagnostics, including checking for trouble codes and performing voltage and continuity tests, to accurately identify the cause of the issue.

Frequently asked questions