How to Test Fuel Pump Relay How to Test Fuel Pump Relay

What You'll Need
Ohmmeter or multi-meter
12V battery or voltage regulator

Buying a car is a tremendous investment, so when your gas mileage becomes an issue, you want to take it seriously. While there could be a few causes for poor gas mileage, a failing fuel pump relay is one of them.

Sometimes, you might not even realize that you have a bad fuel pump relay until you notice bigger issues, like your car engine not starting; therefore, it's smart to test it once in a while. You can spend money to have someone else test your fuel pump relay, or you can test it yourself.

Testing the relay of a fuel pump is relatively simple, as it does not have many parts. The most common parts to burn out or break include the contact and the coil. When either of these begin failing, the current to the electrical circuit will be also fail. This means your fuel pump will cease to function properly.

Check out the following steps to troubleshoot your fuel pump.

Step 1 – Locate the Fuel Pump Relay

First, make sure that you have enough light and room to work. Then, open your vehicle's hood and find the fuse panel. The majority of vehicles made today have the fuel pump relay located near here, and the fuel pump relay should look like a small plastic box with four to five electrical terminals.

However, some fuel pump relays come in different shapes and sizes, so it’s best to locate your manufacturer’s diagram if you’re having trouble finding your fuel pump relay. You may have to explore the engine compartment more thoroughly, or you may find it under the dashboard. The fuse box should be clearly marked on the back or inside of itself.

Step 2 – Remove the Fuel Pump Relay

Unplug the fuel pump relay, but do not break the cover and connecting tabs. Place it on a work surface.

Step 3 – Identify the Components

Generally there are four pins (terminals) on the fuel pump relay. One is for input voltage, one is the ground pin, one is the load pin that goes to the fuel pump, and one goes to the battery. To figure out which pin is which, there will usually be numbers on the bottom of the relay that indicate the pin positions, or you can locate a wiring diagram from your relay’s specific manufacturer.

Step 4 – Set up the Multi-meter or Ohmmeter

Whether you are using an ohmmeter or multi-meter, you'll need to set it to resistance mode.

Connect your multi-meter or ohmmeter probes to the relay. One probe should connect to the pin that goes to the fuel pump, and the other should connect to the pin that goes to the battery.

Step 5 – Testing the Fuel Pump Relay

You want to use either a 12V battery or voltage regulator to test the relay. Connect your ground connection on the power supply to the ground pin on the relay.

Touch the power supply's trigger to the input pin. The relay will close, and you should get continuity between the two pins that the meter is connected to.

You should also hear a clicking noise coming from the fuel pump relay. This noise is the solenoid inside the relay pulling it shut to connect the two posts together.

If your meter does not show continuity from the fuel pump pin and the battery pin, or if you do not hear a clicking from the fuel pump relay, you need to replace your fuel pump relay.

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