Hey guys...I have a constant humming sound from the rear of my 2000 QX4. It sound slike its coming from the gas tank. It has never been present before, and it wont go away. any ideas what this might be? Seems to louder on the drivers side by the rear wheel.
Thanks for the help.

Swap your fuel pump relay for an identical colored one, see if it goes away. If it does, you have a bad fuel pump relay.

Towncivilian wrote:Swap your fuel pump relay for an identical colored one, see if it goes away. If it does, you have a bad fuel pump relay.

Thanks SO much Town....you are the only one that helps me out! I truly appreciate it.
I'll try it out, and let you know.
Thanks again!

How much for a Fuel Pump Relay, and is it hard to replace, and where is it?

The fuel pump relay will be in one of the fuse boxes in the engine bay and will be clearly labeled on the cover of the fuse box. A replacement relay from the dealer is probably around $25, or cheaper at a junkyard. It should come out fairly easy with the aid of a flathead screwdriver to push down the retaining clip.

Towncivilian wrote:The fuel pump relay will be in one of the fuse boxes in the engine bay and will be clearly labeled on the cover of the fuse box. A replacement relay from the dealer is probably around $25, or cheaper at a junkyard. It should come out fairly easy with the aid of a flathead screwdriver to push down the retaining clip.

OK...thanks you SO SO much!! I'll try it tomorrow and report back.

I'm curious as well. I had this happen a few days ago when my mechanic was fixing my loose post-muffler. I turned the car on, then off after a few seconds and it went away. Weird.

The humming sound is probably the fuel pump itself.
It should come on as soon as you turn on the ignition.
It has to build up fuel pressure to start the engine.
If you just leave the key in the on position, but don't start the engine, it should shut off when it reaches the proper pressure.
If the pump is on all the time, then it's a problem for sure.
If that's the case, I'd follow Town's suggestion regarding the relay.
Also, it's never a good idea to run on a low or almost empty tank.
The fuel pump is submerged in the gas, and the gas acts as a lubricant and cooler.
Running on empty will shorten the life of the pump.

Brewcity wrote:

Towncivilian wrote:Swap your fuel pump relay for an identical colored one, see if it goes away. If it does, you have a bad fuel pump relay.

Thanks SO much Town....you are the only one that helps me out! I truly appreciate it.
I'll try it out, and let you know.
Thanks again!

Town is a rock star!!!

The fuel pump is more likely to be cooled by the passage of gasoline through it, not its immersion in it.

I have the same problem on my 99 QX4. I turned off the engine and walked away hearing a buzzing sound from the fuel tank. Engine off with no key in ignition. It would hum for up to 15 minutes. It goes away when I open the fuel cap.

I'll try the relay switch.

Ive been trying to solve this problem as well. My car started doing this a couple weeks ago. Only when I drive it for a while and its good and warmed up do I hear the fuel pump running after I shut it off. Short trips it doesnt happen. My theory is that the coil in the relay is fragile after 20 years of use and doesnt handle heat like it used to. Just ordered mine for under $20 at NAPA supposed to be in tm morning. Ill let everyone know if it fixes it

Do u have a part number for the napa part u ordered?

I sure do. The one I got is ECH AR363. So far so good but Ive only made 2 5 mile trips today tho and it wasnt real common that it would act up on short trips.

I thought it worth mentioning that I did hear the fuel pump after I shut the car off today. If I get to the bottom of this Ill post what I did to fix it.

Just wondering if anyone concluded for sure that the relay is the fix for this issue. Thanks

The relay did not fix my issue. I would recommend checking the resistance across your injectors as I found out I had a stuck injector and replaced that and havent noticed the sound yet. I will keep this thread bookmarked and let everyone know if I do hear it again tho

Lets get this figured out. Several times in the past week when I get home, the fuel pump is humming when I shut off the car. Then each time I went and released the gas cap, the sound would stop. There is vacuum in the gas tank until the cap is released (I suppose it could be pressure instead of vacuum but vacuum makes more sense since the fuel has been getting sucked out of tank). I think this disproves the fuel relay theory, it may not be electrical related. Has anyone tried to replace the gas cap? Maybe the vents in the gas cap are not functioning? What are the vents in the gas cap supposed to do? Ideas appreciated......

It is common for gas caps to have their part numbers updated/superseded. It wouldn't hurt to purchase a new OEM cap to see if that changes anything. I had to replace my mother's '07 Altima's gas cap (because the plastic tail that clips it into the filler door broke) and the parts guy said it was superseded something like 5 times.

Update: I put on a new OEM gas cap, and same thing. It is humming after I shut off the car, then I loosen the gas cap and the humming stops. So the fuel relay and gas cap theories have been eliminated - any other ideas appreciated....

Perhaps one of the EVAP solenoid valves is operating when it shouldn't be? Though I'd think that would usually trip a code.

I checked for TSBs and found nothing related to this sound. Perhaps it's time for dealer diagnostics?

I have this too....


Tried the gas cap replacement...Still hummed...

Tried replacing the evap canister valve.... Still hummed...

Humming stops when you open the gas cap....

I'll be checking the evap solenoid....

P1456 code returns after each time I've cleared the code... Been dealing with this for a long time. I love the way the dash looks without the SES illuminated so would love to fix this.

There is a lengthy diagnostic procedure starting on EC-623 of the FSM, try following whichever steps you can to see if that narrows any possible cause down for your P1456 code. I checked for TSBs regarding P1456 and there were none, except for one revising the DTC confirmation procedure to include use of a smoke machine if one is available.

According to the service rep at my local dealer, this humming sound is "normal" and comes from the VCV pump (vacuum check valve). He says it gradually gets louder with age, and at some point it would be a probably be a problem if it gets too loud. I have 107k miles and I'm going to pretend it's not too loud.

My '01 QX4 is having the same buzzing noise under the drivers side (I think). This happens when I turn the key to accessory, it doesn't seem to affect starting. I bought a replacement fuel pump relay and replaced both the first and second relay with the new one, but no luck with stopping the buzzing. Should I try to replace both relays (Fuel Pump 1 and Fuel Pump 2) to see if that stops it? Would both relays go out if that was the source of the problem?

The fuel pump should not turn on until the ignition switch is in the "on" or "start" position.

So I think you need to verify the noise is indeed coming from the fuel pump. Easiest way to do that is to turn your key to the accessory position so your noise is present, and pull the fuel pump fuse under the dash and see if the noise stops.

I pulled the fuel pump fuse when it was in accessory, the buzzing doesn't stop. Any other possibilities to what it could be?

The only thing I can think of are some valves in the evaporative control system. Your evap canister and some valves are behind the rear tire on the drivers side - there is a cover over them.

Go to the service manual here: http://www.nicoclub.com/FSM/Pathfinder/2001/

Then open section EC, go to page 605. There is a diagram of the parts at the top of the page.

I'm afraid you will have to get under the car and find the exact location of the noise. If that is where the noise is coming from, you should be able to determine which valve is running by putting your hand on it.

Hey mate I found out it was my rear whiper motor buzzing or humming where my car was turned off I have a Nissan Dualis/QASHQAI this only happened whiled the car was supplying electricity after opening a door it would happen for maybe 15minutes hard to sleep next to I unplugged it one screw driver undoo the screw for the rear plastic in the handle then with a flaty just wiggle pop every clip off and the rest of the shell off and unplug it duno temp fix sorted anyway

Hey mate I found out it was my rear whiper motor buzzing or humming where my car was turned off I have a Nissan Dualis/QASHQAI this only happened whiled the car was supplying electricity after opening a door it would happen for maybe 15minutes hard to sleep next to I unplugged it one screw driver undoo the screw for the rear plastic in the handle then with a flaty just wiggle pop every clip off and the rest of the shell off and unplug it duno temp fix sorted anyway