Automotive Fuel Pump Relay

Category: Auto Tuning

fuel pump relay 

 If your fuel pump is not working there is a possibility that your fuel pump relay is bad. When you turn the ignition key forward the coil inside the relay is energized. When the coil is energized you can generally quietly hear the fuel pump buzzing for a few seconds. The fuel pump will come on before the engine has a chance to start up so that the fuel system will be pre pressurized. If the relay has gone bad the fuel pump will never come on. If you don’t hear the fuel pump turn on, look under the hood, probably inside the fuse panel to locate the relay. The air conditioning circuit will probably use a similar relay. If the relays are the same, you can swap the two to test the fuel pump relay.


If swapping relays works you will need a new relay to replace the bad one. If you don’t have a second relay you can test the relay. A relay separates a high load circuit that needs many amps and uses a separate low amp coil circuit to activate the high load circuit. As you can see in this picture there are two circuits. There are four numbers on the bottom on the front of this relay. These numbers will match with numbers on the bottom of this relay next to the connection blades. The image on the front of this relay is a blueprint of how it works. The outer numbers that have the red arrows pointing to them is the main high amp part of the circuit.

 In the image above you will see a square with a diagonal line running through it, this represents the coil circuit. The center numbers are part of the coil circuit and will switch the relay on. The relay will work when 12 volts dc is applied to these inner pins. If you follow the lines that extend from the outer numbers you can also see that there is a gap in the line. This gap represents that these two pins are not connected or normally open in this circuit. The circuit will close and allow voltage across it after the coil circuit is powered. To test it apply 12 volts the the coil circuit then place an ohm meter on the high amp circuit. Select any ohms setting on your ohm meter. Because the coil is powered you should see numbers close to zero displaying on the meter. When you disconnect the 12 volts to the coil circuit the numbers on the meter should disappear and show nothing. This will happen if the relay is working correctly. If nothing happens then the relay needs to be replaced.