If your vehicle starts to slow down on its own, the engine fails to start, or your fuel mileage drops, check the fuel pump relay. A fuel pump relay controls the current of the fuel pump as it pumps gas to the engine.
The first parts on the relay to malfunction are commonly the coils or the contacts. A fuel pump relay doesn't have many parts, so a beginner without any knowledge of repairing vehicles can test it. Here are some tips to test a vehicle fuel pump relay.
Prepare to Work
For this project, you need:
Park your vehicle in a lighted area on a flat surface. Open the hood, and look for the fuel pump near the fuse panel in the engine compartment or under the dashboard on the passenger side. The fuse panel should be marked.
The fuel pump relay is a small plastic box that commonly has four wires connected to it. Check the diagram of your fuel pump relay in your owner's manual if you can't find the fuel pump relay.
Test with a Multimeter
Disconnect the fuel pump relay, taking care to not break the plastic tabs. The multimeter tests for continuity by measuring ohms, or units of electrical resistance. Set the multimeter on the lowest setting, which is RX1 (resistance times one).
Touch the test probes to the relay coil. You should get an infinite reading. If you get a reading less than infinite, which is one (1.000) on a digital multimeter, or the needle doesn't move on an analog multimeter, the fuel pump relay coils have shorted, and the relay needs to be replaced.
Touch each of the four contacts with the multimeter test probes. If you get a reading of zero, or a reading in the hundredths or thousandths, replace the relay. If the multi (meter shows infinite, or OL (overloaded), which indicates an open circuit, proceed to test with jumper cables.
Check with Jumper Cables
Attach one end of a fused jumper wire to a ground contact on the fuel pump relay, and the other end to the positive terminal of the auto battery, which is commonly red. Connect the end of a regular jumper cable to the other ground contact on the relay, and the other end to another good ground wire, such as an engine wire.
Listen for a click from the fuel pump relay when you connect the cables. If you don't hear a click, swap the wires and listen for the click again. If you still don't hear a click, replace the fuel pump relay.
Testing a fuel pump relay yourself saves money. If you don't feel comfortable testing a fuel pump relay, or the relay needs replacing, visit an auto repair shop.
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