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Dan, Technician
Category: Nissan
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Experience:  Independent Shop Experience, 2 Year Automotive Diploma, & Access to Information Database
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Symptoms of a bad fuel pump or fuel pump relay.

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What are the symptoms on a bad fuel pump or a bad fuel pump relay?

If you have a bad fuel pump the vehicle may stall or not start and usually does not show a check engine light. If the fuel pump relay has failed, you will not hear the pump hum when you turn the key into the on position or hear the relay click. The only way to be certain is connect a fuel pressure tester and make sure vehicle has proper fuel pressure.

Customer: replied 8 years ago.

Lately, it doesnt start more than it does. It may not start for 7 days but on that 8th day, it will start up and possibly on the 9th day as well.

Does this sound like it is the fuel pump/relay or something else?

Is your check engine light on? If not, a fuel pump would be a likely problem. The only way to be sure is to do a fuel pressure test.

What year, model, make and engine size is your vehicle?

I''ll look up specifications and see if there is any common problems.

Customer: replied 8 years ago.
Well, my service engine light is on. The car is actually an infiniti I30, 1998. 6 cyl engine, 3.0 ltr

The most likely problem is a failed camshaft sensor or mass airflow sensor. Test during no start condition. You can backprobe the wires at the camshaft sensor and check for AC voltage while cranking. If no voltage replace.

Here are troubleshooting steps along with location pictures. If you wanted to make it easy on yourself, drive the car to a parts store next time it runs, have them hook it up on a scan tool and give you the trouble code. That will give a more exact direction in where to locate the problem.

1. At the Mass Air Flow (MAF) sensor, verify that the connection is good and the Black/White wire has battery voltage and the Black wire has a good ground.

2. Check the signal wire or the White wire, the voltage should be approximately 1.3 to 1.4 volts at idle. Always verify that the White wire is not intermittently grounding out. If the signal voltage goes high or low in relation to the airflow and the harness and connection are good, then suspect a faulty MAF sensor.

troubleshooting a failed camshaft sensor or mass airflow sensor

Dan and other Nissan Specialists are ready to help you

Fuel Pump Relay Symptoms 

The fuel pump relay is an electrical element that is in almost every vehicle designed with an internal combustion engine. Fuel pump relays are in the engine’s fuse box; their job is to control the power to the fuel pump.

Fuel pump relay appearance

The fuel pump relay is relatively small in appearance but is a large supporting factor to the fuel system. Basically, the fuel pump relay is a small black plastic box with a wiring harness attached to the bottom.


How the fuel pump relay works 

When the ignition is first started or turned on, the fuel pump relay activates. Then, it sends an electrical current to activate the fuel pump. Once the fuel pump is activated, it begins to pump gasoline so the starter engages and triggers the vehicle to start and continue to run. The fuel pump remains on while the car is running, but once the car starts, the fuel pump relay’s job is done and shuts down.

The oil sending unit gives the fuel pump power and sends oil pressure data to the vehicle’s computer. When the key is off and the engine shuts down, the fuel pump relay switches on again for a short period to turn off the electrical power to the fuel pump. This ensures that the fuel is no longer pumping through the gas tank and fuel lines.

Fuel pump relay facts

A fuel pump relay is one of the fuel system’s primary components and works much like an auto fuse. Similar to a conduit, it transfers power to the fuel pump and controls the amount of power sent. It requires a lot of electrical currency to function properly. It is designed to withstand a substantial amount of power. Nevertheless, if too much electrical current gets distributed to the fuel pump, the wiring could become too hot, damaging or ruining the fuel pump. The engine control module controls the fuel pump relay.

There are three main components of the fuel system in a vehicle.

  • Carburetor: Mixes air and fuel for combustion
  • Fuel tank: Where the gasoline is stored
  • Fuel Pump: Feeds gas through a fuel line from the gas tank to the fuel injectors or carburetor

Fuel pump relay location 

The fuel pump is located underneath the hood and fastened to the internal firewall. The firewall is a solid, fireproof barricade between the engine housing and the cab of the vehicle. In some vehicles, the fuel pump is in the gas tank and is often attached close to the fuel level gauge. In some cases, the fuel pump relay is on a fender cover or the steering column. 


Checking the fuel pump can be dangerous if you are not familiar with automotive repair. If you choose to tackle fuel pump relay problems on your own, you should keep in mind the dangers of working around gasoline.

Before buying a fuel pump relay for your car, familiarize yourself with the location and the type of fuel pump relay you need.