4 Easy DIY Steps How to Test Fuel Pump Relay

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This article will show you how to test fuel pump relay on your car so that you can save money by fixing potential problems early.

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Photo: Scott Garvey

Most electrical components in vehicles or machines are activated by a relay. As a car owner, you will eventually experience problems in the fuel pump relay.

If your car is not starting or running smoothly, it may be worth checking out the electrical system for any signs of trouble.

It’s important to diagnose these issues as soon as they arise and to take care of them before they worsen and become too expensive.

How do you check if a fuel pump relay is bad?

Relays are used to turn electrical currents on and off. They help extend the life of switches by preventing high amounts of electricity from going through a switch.

If you experience that the engine stalls, do not start, or you can’t hear the short buzzing sound from the fuel pump, you may have a bad fuel pump relay.

Related: Common Problems After Changing Fuel Pump – Top 5 Issues

You can diagnose the problem by testing it with a multimeter. We highly recommend the Fluke 88 V/A KIT Automotive Multimeter Combo Kit for advanced users.

It is designed for auto enthusiasts who need accurate results when testing the likes of fuel injectors and hybrid engines.

But if you consider yourself a newbie to car troubleshooting, consider the following options:

How to test fuel pump relay with a multimeter

The primary tool you’ll need is a multimeter to check if a relay is bad. Here’s a step-by-step process of how to check a fuel pump relay using a multimeter.

What you’ll need:

  1. Multimeter
  2. Contact cleaner
  3. Fuel pump relay diagram

Step-by-step guide:

Step 1. Locate the relay from the fuse box and remove the relay from its socket.

Refer to your owner manual to find your fuel pump relay. Usually, you can find it inside the power center under the hood or the dashboard and sidekick panels.

Tip: Learn the basics of the multimeter before checking your car.

Step 2. Check the fuel pump relay for any sign of corrosion

Visually inspect the fuel pump relay from its outside. Look for any signs of corrosion. 

Corrosion can cause a part to malfunction, so you might want to check this first and clean it with a contact cleaner.

Step 3. Check if for a blown fuse

Set the multimeter to measure DC voltage and check the number 85 position in the fuse box where the relay plugs.

If there is no 12 volts reading, check if the fuse is blown. If it’s intact, check the continuity between the power circuit terminals.

Step 4. Check for continuity between the terminals

To do this, set the multimeter to continuity mode or the lowest range on the Ohms scale. 

Connect one lead to one of the power circuit pins while the other lead to the power terminal.

If you observed the following, your relay’s power ins have shortened:

  • Zero ohms or resistance value in the hundredths or thousandths
  • You hear a beeping sound

Note: Some relay power switches come normally closed and should open when energized. They usually have 30 and 87a numbers, so always check the diagram on the relay.

If this is the case, then the zero ohms and the beeping sound means that the fuel pump relay is in good condition.

Here’s a Youtube video on how to test the fuel pump relay from Advance Auto Parts to help you out:

Here is a fuel pump relay diagram to help you identify the pins:

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Can you test a fuel pump relay without a multimeter?

Yes. you can still test the fuel pump relay without a multimeter. However, this method is not as accurate.

Below are the methods how for testing fuel pump relay without a multimeter:

First, you can use a test light to check if it is functioning. Use a high-impedance test light to check if the relay is receiving power.

Alternatively, you can switch the keys from OFF to ON and listen for a clicking noise and the fuel pump short buzz sound. The buzzing sound also indicates that the pump pressures the fuel system.

Related: How to Check Fuel Pressure Without Gauge in 2 Easy Methods

Can you bypass a fuel pump relay?

It is possible to check this just to be sure quickly. Simply attach the relay’s 87 and 30 points with a wire or cotter pin, then test the connection by turning on your car keys.

The component should begin working. This temporary repair for emergencies keeps the machine running a while until the correct part can be installed.

Conclusion

If you experience that the engine stalls, do not start, or you can’t hear the short buzzing sound from the fuel pump, it may be a bad relay. Although we do not set aside the possibility that it could be due to a bad fuel speed sensor.

You can diagnose this by testing it with a multimeter. Yes, it is possible to test without one, but a test light works just as well.

Can I bypass it? It’s possible to check this quickly if you want to ensure everything is working correctly and there isn’t anything else going wrong in your car before replacing a fuel pump relay.

Investing in a multimeter will help make sure your diagnosis process goes smoothly.

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