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How to Replace the Fuel Pump Relay?

Author: Apogeeweb Date: 21 Jul 2021  296

bad fuel pump relay


Ⅰ Definition of Fuel Pump Relay

Ⅱ Function of Fuel Pump Relay

Ⅲ Application of Fuel Pump Relay in Vehicles

  3.1 The working principle of automobile relay

  3.2 The function of automobile relay

Ⅳ The Location of Fuel Pump Relay

Ⅴ Symptoms of a bad Fuel Pump Relay

Ⅵ How to Replace the Fuel Pump Relay 

  6.1  Part 1: Removing the fuel pump relay

  Step 1:

  Step 2:

  Step 3:

  Step 4:

  Step 5:

  Step 6:

  Step 7:

  Step 8:

  Step 9:

  6.2 Part 2:  Installing the new fuel pump relay

  6.3 Part 3: Checking for fuel pump relay operation

  6.4 Part 4: Test drive the vehicle

Ⅶ  Frequently Asked Questions about Fuel Pump Relay Failure Analysis


Ⅰ Definition of Fuel Pump Relay

As most people are familiar with, the fuel pump is a component inside the fuel tank that enables the combustion engine to run by providing pressure in the fuel lines to push gasoline to the combustion engine.  The fuel pump can fail for a variety of causes, one of which is a less well-known problem with the fuel pump relay.


A fuel pump relay is a compact unit with many sprockets on one side that are clipped onto the ignition system and is covered in a plastic container. A gasoline pump relay is, in some ways, similar to an automotive fuse in that it is an electrical component. It controls the flow of current to the electric fuel pump, ensuring that the component receives enough power to function properly but not so much that it is damaged. Fuel pumps consume a lot of power, which may cause the electrical system and the pump to overheat  if  it weren't for the relay.

Ⅱ Function of Fuel Pump Relay

In general, the relay acts as a power monitor for the fuel pump, activating it when the ignition is turned on and turning it off when the vehicle is turned off. When the ignition switch is turned to the on position for the first time, the fuel pump can be heard humming. This provides fuel to start the vehicle, and once the vehicle is running, the vehicle's computer sends a signal, and the fuel pump relay turns off. The fuel pump in the vehicle will now be powered by another source, typically the oil pressure sending unit.

The vedio shows that how a fuel pump relay works

Ⅲ Application of Fuel Pump Relay in Vehicles

Automobile relays are composed of a magnetic circuit system, contact system, and restoration mechanism, as indispensable circuit components, such as automobile lights, air conditioners, electric seats, electric doors and windows, ABS devices, etc. have control relays.


3.1 The working principle of automobile relay

The electromagnetic relay applies the principle of electromagnetic induction. When the coil goes through the DC, the coil generates a magnetic field, and the moving iron is attracted to drive the contact reed, which separates the static contacts and closes the moving contacts. The iron core loses its magnetism when the electromagnetic coil current is switched off, the moving iron core is reset by the spring force, the moving contract is unfolded, and the static one is closed.

The contact in the off position is a typically open contact, and the contact in the on position is a normally closed contact when the relay coil is not activated.  Between a normally open contact and a normally closed contact, there is a moving contact called a changeover contact. There can exist one or more ordinarily open contacts, normally closed contacts, and conversion contacts in the same relay.


In most electromagnetic relays, there is only one coil. A text sign is commonly used to identify the relay coil and its contacts, and each group of contacts is identified with a subscript, to illustrate the relay plainly and simply on the circuit.

3.2 The function of automobile relay

By controlling the current of the low-voltage line, the current of the high-voltage line is controlled, and it acts as a current switch. The main function of the car is to start the motor rotation by controlling the large current by small current, thereby driving the rotor of the magneto inside the generator to rotate, giving the ignition Input the ignition pulse signal to make the ignition  generate electric sparks, ignite the mixed gas in the cylinder and do work.


Relays belong to the switch category. It takes advantage of electromagnetic and electrical  and mechanical principles to close or open contacts to drive or control related circuits.


A relay is a control device that is consisted of two parts: a controlled system (input loop) and a control system (output loop) (output loop). The output quantity changes abruptly from zero to a given value (or from a certain value to zero) when the input quantity (electricity, magnetism, light, heat, and other physical qualities) reaches a certain value, allowing the circuit to be controlled, protected, regulated, and transmitted.

The Location of Fuel Pump Relay

The majority of fuel-pump relay units are found beneath the dashboard, near the steering wheel. In certain circumstances, the unit is positioned near the engine's firewall or in the location where the steering column is attached. The fuel pump relay's end is usually at the center of the floorboard, under the carpet in the front area of the passenger or driver's side footwell. The fuel pump relays can be found in a variety of locations depending on the vehicle.


If you have your owner's manual (and if you don't, you can get a new one from owner Manual), check it and look at the schematic to see where the location is.


This is not an accurate list, it is only for a few models of vehicle. But it contains the most common locations where I've found this component.


If you need to find the exact placement of the fuel pump relay quickly, consult your service manual.


Figure1: the general location of fuel pump replay

• Driver’s Side Kicker Panel

Nissan prefers to hide the fuel pump relay beneath a plastic cover near the brake or gas pedal, which is held in place by a couple of bolts. To get to the part, simply remove the bolts and the cover!


•  Near The Fuse Box

I've seen it in the fuse box or very close to the fuses in numerous Mazdas and Toyotas.


• Passenger Side Firewall Near Dipstick

The pump relay is located behind the oil dipstick near the strut/shock housing on older Mitsubishis, particularly the Evolutions.

Symptoms of a bad Fuel Pump Relay

• Engine stalls

An engine that suddenly stalls is one of the most obvious signs of a problem with the fuel pump relay. If the fuel pump relay fails while the vehicle is in operation, the fuel pump will lose power, causing the engine to stall. A malfunctioning relay may allow the engine to be restarted after a short period of time, but a relay that has fully failed will not.

• Engine does not start

A non-starting engine is another indicator of a malfunctioning fuel pump relay. The gasoline pump will be left without electricity if the fuel pump relay fails. When the key is turned, the engine may still crank, but it will not start owing to a lack of fuel. This symptom could be caused by a variety of different problems, so having the vehicle professionally assessed is essential.

• Loss of Power

If the automobile suddenly loses power while driving or slows down for no apparent reason, the gasoline relay could be to blame. This does not necessarily imply that the vehicle will stall.


For a short period of time, the vehicle will continue to run normally. However, if you encounter a sudden lack of power while driving, you should get your automobile inspected and repaired immediately, as there is always the possibility that the car will come to a halt again, leaving you stranded in the middle of the road.

No noise from the fuel pump

When the key is turned on, there is no noise from the fuel pump, which could indicate a problem with the fuel pump relay. Most fuel pumps emit a low-volume hum or whine that can be heard from inside the vehicle, or from outside the vehicle, near the fuel tank, if you listen carefully. If the fuel pump relay fails, power to the fuel pump is cut off, rendering out operation and, as a result, silent when the ignition is turned on.


The gasoline pump relay is a relatively simple component, yet it is important to the vehicle's proper operation. If you notice any of the above symptoms or suspect that your fuel pump relay is failing, have your vehicle inspected by a professional to determine whether the component needs to be replaced. 

Ⅵ How to Replace the Fuel Pump Relay

6.1  Part 1: Removing the fuel pump relay

Materials Needed
• Needle nose plyers
• Ratchet with metric and standard sockets
• Wheel chocks

Step 1:

Turning on the ignition key ,wait for the gasoline pump to operate.
Also, listen for any buzzing or clicking noises coming from the fuel pump relay.

listen-noise Figure2: listen  noise from the relay

Step 2:

Start the engine. Check that there is oil pressure.
An oil light may be the lone signal on some automobiles. When the indicator light turns off, there will be oil pressure.

oil lightFigure3: check the oil light on dashboard


Step 3:

Park your vehicle on a flat, hard surface.
Make sure the transmission is in a park (for automatic transmissions) or first gear (for manual transmissions) (for manuals).

parkingFigure4: Parking your vehicle

Step 4:

Place wheel chocks around the tires.
Because the rear of the car will be raised, the wheel chocks will be around the front tires in this situation.
Engage the parking brake to lock the rear tires from moving.

wheels-wheel-chocksFigure5: Place wheel chocks around the tires

Step 5:

Install a nine-volt battery saver into your cigarette lighter.
This will keep your computer activated and your vehicle's settings current. It's fine if you don't have a nine-volt battery saver.

battery-boxFigure5: Install a nine-volt battery

Step 6:

Open the vehicle’s hood to disconnect your battery.
Remove the ground line from the negative post of the battery to turn off the power to the fuel pump and sending unit.

openFigure6: open your engine and disconnect your battery

Step 7:

Look in the engine area for the fuse box. The fuse box's lid must be removed.

fuse boxFigure7: Find the fuel box

Note: Some fuse boxes are secured with hex screws or bolts and must be removed using a ratchet. Clips hold the other fuse boxes in place.


Step 8:

Locate the fuel pump relay using the diagram on the fuse box cover.

Using the schematic on the fuse box cover, look for the fuse for the fuel pump relay when you open the fuse box.


box_coverFigure8: Locate the fuel pump


Step 9:

Remove the fuel pump relay from the fuse box. Pay attention to how the relay comes out as the new one needs to go in the same way.
If your fuse box cover doesn't have any schematics on it, you can look up the engine compartment fuse box diagram in your owner's handbook. The number adjacent to the fuel pump relay is usually stated in the owner's manual so you can discover the number on the fuse box.

Note: You may need to use a pair of needle nose players to pull out the fuel pump relay.

How_to_replaceFigure9: Remove the fuel pump relay

6.2 Part 2:  Installing the new fuel pump relay

Materials Needed
Replacement of fuel pump relay

Install relay. Install the relay into the fuse box the same way  the old relay was removed.


Put on the fuse box cover. Snap it into place.
Note: If you had to remove screws or bolts from the cover, make sure you put them back correctly. They will strip out if you tighten them over.


Remove the fuel cap from the fuel tank.  Replace the gasoline cap and double-check that it seals properly.


6.3 Part 3: Checking for fuel pump relay operation



Reattach the ground line to the negative post of the battery. Remove the cigarette lighter's nine-volt battery saver.

Wait for the gasoline pump to turn on.



Tighten the battery tightly. Ensure that the connection is good.


Turn the ignition key on. Listen for the fuel pump to activate.
When the fuel pump stops generating noise, turn off the ignition. Restart the engine and listen for a buzz or click from the fuel pump relay. To experience the buzz or clicking action, you may need to have another person touch the fuel pump relay.
Note: Before starting the engine, turn the ignition key on and off three or four times to ensure the fuel rail is full of fuel.


Start the engine by turning the key to start. During the cranking time, keep an eye on how long the start will be engaged.Note: Most modern vehicles will not start up until the oil pressure has built up.


Wheel chocks should be removed from the wheels. Place these in a safe place.


6.4 Part 4: Test drive the vehicle


Drive the auto around the block. During the test, listen for any unusual noise from the fuel pump or fuel pump relay.
Also, immediately accelerate the engine to ensure that the fuel pump is working properly.



Monitor the dash for any engine lights.
If your engine light turns on after replacing the fuel pump relay, you may need to have the fuel pump assembly diagnosed or there could be an electrical problem with the fuel system. If the problem persists, you should contact one of Your Mechanic's qualified technicians, who will test the fuel pump relay and diagnose the issue.



Ⅶ  Frequently Asked Questions about Fuel Pump Relay Failure Analysis

1. What causes a faulty fuel pump relay?

A gasoline pump relay might fail due to dust, electrical power surges, and other issues. Dust and rapid voltage surges can degrade the performance of a fuel pump relay, causing an engine to fail. Passenger Side Firewall Near Dipstick.


2.  Will a fuel pump work without a relay?

What is a Fuel Pump Relay, and What Does it do? A fuel pump relay is a plastic covered part connected to the fuel pump. It is one of the most important parts of your vehicle. Without the fuel pump relay, you won't even be able to drive your vehicle.


3. Can AutoZone test a fuel pump relay?

AutoZone makes checking fuel pressure easier than ever. ... While testing does entail some work, few things are more rewarding than successfully troubleshooting your fuel pump relay. And with a fuel pressure test gauge from AutoZone, it's easy.


4.  How does a car act when the fuel pump is going out?

You'll notice a decrease in fuel efficiency, acceleration and power in your vehicle if your fuel pump is damaged. The low pressure caused by a faulty fuel pump means your engine isn't getting the fuel and air mixture it needs to give your car that regular power. Whining in the backseat.


5.  How long does a fuel pump relay last?

Over time, the fuel pump relay can begin to show signs of wear and will have to be replaced. The fuel pump relay is designed to last the life of the car, but due to the grueling conditions it is exposed to, it will not usually last that long.


6. Where is the fuel pump reset button?

Look for the fuel pump switch or inertia switch. This is a small box with a plastic button on top and an electrical connector at the bottom. On some vehicle models, this will be located in the luggage compartment. Look on a side panel for a small, round button which you can pry off with a small screwdriver.


7. Will a car start with a bad fuel pump?

If your vehicle's fuel pump cannot get gas from the tank to the engine, you will have trouble starting your car. The car will struggle to start and run because the pump cannot push enough gas through. A worn pump loses its pressure and the engine is being starved of gasoline.


8. What would cause a fuel pump not to get power?

If you there is no power to the fuel pump or the relay, then there may be a possible electrical issue with the vehicle. ... If there is an issue with the switch or the circuit, perhaps a wiring problem, then power to the fuel system may be cut off.


9. Will a bad fuel pump give a code?

Bad Fuel Pump, Fuel Pressure Sensor Can Trigger 'Check Engine' Light, P0087 Code. ... The light is part of your vehicle's on-board diagnostics (OBD) system and can indicate anything from a loose gas cap to a major repair like a catalytic converter.


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