Fuel Pump Relay Failure

Fuel Pump Relay Failure

Aaron U Smith writes on automotive fuel delivery systems including fuel pump problems and fuel pump replacement

A fuel pump relay is an important part of a fuel delivery system that controls the supply of fuel from the fuel pump while starting of the engine. It switches the fuel pump on when the ignition is turned on and shuts off when the oil pressure takes over running of fuel pump. When the vehicles ignition is turned on, the magnetic coil with an open contact gets activated, thereby closes the circuit between the fuel pump relay and the terminal of the electronic control mechanism. Thus the relay generates the required electricity for the fuel pump to run and supply fuel for the engine to operate. When there is enough oil pressure in the engine to run the fuel pump, the relay shuts off automatically from the circuit. It again comes into action when the engine is turned off to induce the fuel pump to stop working.

The fuel pump relay is usually enclosed in a plastic fuse box located underneath the dashboard, near the steering. In some car models, it is located in the engine compartment near the firewall. The most common issues that can cause failure of a fuel pump relay are the coil and the contact terminals connecting the ignition assembly. Any fault with the relay parts, causes issues with fuel pump working and the engine would not receive fuel while starting of the vehicle. Normally, when the ignition is on, the driver would hear a clicking noise of the activated relay from the engine compartment. If no noise is heard, it is an indication that there are issues with fuel pump relay.

Check For Symptoms • Engine Cranks But Doesn’t Start The engine makes cranking noise but doesn’t start due to lack of fuel pumping into the engine. Sometimes the vehicle would start but you would notice delay in the starting of the engine. This is because the engine has no fuel supply at ignition and the vehicle will start after a while when the motor pumps up sufficient oil pressure to send electricity to the fuel pump and run it.

• Inconsistent Engine Functionality When the fuel pump relay fails there will be no supply of power to the fuel pump.

Though the vehicle starts after a while later, there will be loss of power while driving and the engine may completely come to a stall. This is because there is no continuous supply of fuel from the gas tank to the engine.

• Absence of Sound From The Fuel Pump Another symptom is you would not hear fuel pump working when the vehicle is turned on. A low volume humming noise of the fuel pump functioning is typically heard when the ignition is turned on. If the fuel pump relay fails, the fuel pump will not switch on and hence no noise is heard by the driver.

Replacing Fuel Pump Relay Once you suspect an issue with fuel pump relay, it’s not a good idea to neglect it.

The relay must be replaced otherwise the problem may escalate other issues causing damage to car’s ignition system and engine. First you need to locate the fuse box and identify the exact location of fuel pump relay. Since the location is different in different car models, you can check underside of the fuse box engine compartment lid for the diagram showing fuses or relays or refer to the owner’s manual to identify the location. First disconnect the battery by disabling the negative terminal to shut the power off to the fuel pump. De-pressurize the fuel system by removing the cap of fuel tank. Remove the relay, replace it with the new one and reconnect the plug-ins and other fuse connections. Reconnect the battery cables and re-pressurize the fuel system. Make sure the fuel cap is secure and tightly sealed. Now turn the ignition on and let the fuel pump get activated.

You will hear fuel pump working when the engine is started. Turn off the ignition and repeat the process for several times until the fuel enters into the fuel rail. If possible test drive the vehicle to check if any other issues are persisting within the fuel delivery system.

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