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Faults in the fuel pump can cause problems with starting the engine, and it is not always possible to guess what the cause is.

The relay is primarily responsible for supplying and disconnecting power from the electronic control unit to the gasoline pump.

If you hear strange noises, if the pump doesn’t pump fuel when you turn the ignition key, the may be related to the relay.

Signs of the relay malfunction

Let’s go over the signs of malfunction in the fuel pump relay. Where is the fuel pump relay located? The location of the relay varies depending on the make of the vehicle. Most often, it is located under the hood, in the fuse box and relay box.

Defects of the fuel pump relay:

  • Breakage of the relay circuit.
  • Oxidation or breakage of the wires.
  • Deformation of the housing.
  • Melting at the contact areas.
  • Carbon between the contacts.

Causes of relay failures

Let’s take a look at possible relay failures. The very first and most obvious cause of relay failure is natural wear and tear. Each part has its own lifespan, and when it passes, it breaks.

If the relay was relatively new, you should look for faults in the list below.

  • Factory defect (not common, but it can happen).
  • Moisture ingress (the relay will look very rusty).
  • Breaking of the electrical circuit or a short circuit.
  • Capacitors have failed.

Signs and symptoms of fuel pump relay failure

Let’s start with the fact that the control of the gasoline pump through the relay occurs according to the following general scheme: the driver inserts the key into the lock and turns on the ignition. Also on some cars, the device serves as a kind of engine speed limiter.

If the engine revolutions are close to the maximum and begin to exceed the permissible threshold, the gasoline pump is disconnected through a relay.

The gasoline supply is stopped, RPM is reduced, and then the element again supplies power to the pump. If the relay malfunctions, then the gasoline pump may not be powered.

The second option is that the pump buzzes or hums constantly, that is, it does not turn off a few seconds after creating the necessary pressure in the fuel line. In the first case the engine often fails to start as the pump is not pumping and there is no petrol in the fuel rail. In the second case, the gasoline pump relay is stuck (the gasoline pump relay is not activated) and the battery charge is consumed for the constant rotation of the fuel pump motor.

We would like to add that on some cars it is possible to start the engine even with some malfunctions because the pump relay connection scheme allows the device to work during cranking by the starter.

Main faults related to relays and their causes

SignType of failurePossible causes
When the ignition is turned on there is no sound of running a gasoline pump does not sound when the ignition is turned on.There is no power to the gasoline pump.Short circuit.
The relay is defective.
Natural wear and tear on the part.
Contacts are oxidized, rusty, or damaged.Bad starting, stopping during engine movement. Noise from outside.Water ingress, condensation, short circuit.
The car stopped starting after the installation of
external immobilizer.
Blocking the power to the fuel pump.Incorrect installation immobilizer, or incompatible with the new security system.
The pressure in the fuel system is less than optimal for this car model.The gasoline pump is not pumping properly and does not produce the required pressure.Wiring problems, relay or fuse failure.
fuel pump relay diagnostic

How to understand that the gas pump relay must be checked

You can determine that the relay is faulty by paying attention to the following abnormalities in the operation of the fuel pump:

  • The pump has stopped turning off when it reaches the correct pressure, which is manifested by an unpleasant humming sound.
  • There is no characteristic sound when the ignition is turned on.
    No power to this unit.
  • The engine does not start, as it is not connected to the power supply of the fuel pump.
  • In some models of cars, even when the maximum permissible number of engine revolutions is exceeded, the gasoline pump turns on. But it may not start from the first time, the engine stops, or there are noises coming from the working pump.

How to check the gas pump relay

First, it is necessary to take a test lamp and inspect the fuse. It may simply be blown, so when repairing it is enough to replace this element. Near the fuse is also the fuel pump relay. It is necessary to check the voltage in the area of the control terminals, touching the ground with the other end of the tester.

You can also check with a 12 volt light bulb with a current of no more than 0.25 Ampere.

Do not use a higher wattage, otherwise, the control unit may be damaged.

The bulb is connected between output 86 and 85. After the ignition is triggered, the light bulb should light up. If it does not, then the relay is defective.

Checking the fuel pump relay with a multimeter

1.You need to find the relay

To know how to check the fuel pump relay with a multimeter, you need to find it in your car for a quick analysis. You need to open the hood of the car and start looking for the relay, which is usually located in the fuel pump. The relay may be located near the bulkhead or in the fuse box under the general electrical panel.

Depending on the type of vehicle, you may find the relay as large or small parts. Looking for a relay in your car won’t ruin its performance, but you will be looking for a cheap solution. Special car repair manuals can help you quickly find a relay hidden under the hood.

2. Remove the relay

Now that you’ve found the relay in your car, you can remove it to do a visual inspection to see if it’s working properly. You need to pay attention to corrosion on the relay’s terminals or base, which can damage it. If the relay is corroded, it may overheat, which in turn will cause performance problems.

3. Relay Testing

To find out how to test a fuel pump relay with a multimeter, you can continuously test it for current using its terminals. To see the effect, you need to install a multimeter with a low ohm range or only the continuity option. You need to connect the multimeter terminals to the circuits to see their energy reading.

If there is nothing wrong with your car’s relay, the resistance should be OL or open load and you should not hear an alarm on the multimeter. If you find 0 ohms in the relay resistance, it could mean you have a short circuit. If the relay is not delivering current, it’s time to replace it with a new one.

Quick Tests for Relays

If you’re desperately trying to get your car to start, you should know how to quickly test a fuel pump relay with a multimeter:

  1. You’ll need to connect a jumper wire, which you may have on hand to help a friend, to the relay with the positive battery terminal.
  2. Now is the time to connect the other jumper wire to the negative terminal of the car battery to the relay terminal.
  3. When you connect the second jumper wire to the relay, it should make contact as current flows from both ends. If you don’t hear this contact, you no longer have any reason to doubt the relay and its death from corrosion or factory defect.

If you check the relay with or without a multimeter and find no indication that it is sending current, it needs to be replaced. Repairing a relay can be complicated, so it’s best to call in a technician.

What happens to your car if you don’t check the gas pump relay

The possibility of an emergency situation increases, because the engine may stall while driving on the highway.

It is impossible to predict how a broken relay will behave and at what point it will cease to perform its functions. It may happen that in the morning the car will start after a few times, but in the evening the pump doesn’t respond to the turn of the key.


Problems with auto electrics are not as noticeable as malfunctions of the engine itself, but they are no less serious. Determine that there is a malfunction of the gasoline pump, you can hear when you turn on the ignition. You should check this unit as soon as possible, most often it is not the pump itself that breaks, but its relay. This part is not so difficult to check, and if necessary can be replaced.


🔧 Will the fuel pump run without a relay?

If the fuel pump relay fails, it will cut off power to the fuel pump, which will render it inoperable, and therefore silent when the ignition is on.

🔧 Why does a fuel pump need a relay?

When you turn on the ignition, the fuel pump relay is activated and will supply electricity to turn on the fuel pump.

🔧 How long does a fuel pump relay last?

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.

How to Check a Fuel Pump Relay - Video

David Muench (Carnes Mechanical)

David Muench (Carnes Mechanical)

Hey, I’m David. I’ve worked in a cars store for 6 years. I write reviews and guides, helping people to choose the most suitable technicals and best product for them. I’m happy to finally share my knowledge of the industry here, on CarnesMechanical.

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