How to Diagnose a Fuel Pump Relay


The fuel pump relay is part of the fuel pump and sending unit. The relay itself is a small electrical device with four to five prongs that connects to the battery, the fuel pump and the sending unit. The relay sends a signal to the fuel pump telling it to start drawing fuel in from the fuel tank and pumping it to the engine. Once the relay has been energized, the pump stays on and draws its power from the battery. Over time, the relay may short out, become overloaded from an electrical surge or it can fail simply from age.

  • Put the key into the ignition and turn the key to the "II" position, but do not attempt to crank the engine.

  • Listen for a slight hum or buzzing sound that will last approximately 1 to 2 seconds. This is the fuel pump relay being energized.

  • Open the fuse panel under the dash and check the fuse for the fuel pump and sending unit if you do not hear the fuel pump energize. The fuse for the fuel pump will also supply power to the fuel pump relay. If the fuse is blown, you'll need to replace the fuse and repeat Steps 1 and 2.

  • Have the relay tested by a qualified mechanic or replaced if you completed Step 3 and you were unable to hear the fuel pump relay energize.

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