What's that humming sound? - Kia Niro Forum
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post #1 of 10 (permalink) Old 02-26-2019, 12:23 AM Thread Starter
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What's that humming sound?

I walked into the garage this evening and was surprised to hear a humming sound that seemed to be coming from my car. It seemed rather strange that it would be doing that, because the car had been parked for almost 24 hours. It was not plugged in, air temp peaked around 63 F today, so I kind of doubt that it was a cooling fan. The sound reminded me more of an electric fuel pump sound rather than an electric fan kind of sound, but it seemed a bit louder than the fuel pump sounds I've heard in other cars. I walked around the car to convince myself that the sound was really coming from the car and not from some point outside the garage: I'm convinced that it was, but I couldn't confidently reach a conclusion about which part of the car it was coming from. After about 15 seconds, I opened the rear hatch and about three seconds after that, the sound stopped. Anyone have any ideas?

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post #2 of 10 (permalink) Old 02-26-2019, 07:11 AM
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Originally Posted by deltasmith View Post
I walked into the garage this evening and was surprised to hear a humming sound that seemed to be coming from my car. It seemed rather strange that it would be doing that, because the car had been parked for almost 24 hours. It was not plugged in, air temp peaked around 63 F today, so I kind of doubt that it was a cooling fan. The sound reminded me more of an electric fuel pump sound rather than an electric fan kind of sound, but it seemed a bit louder than the fuel pump sounds I've heard in other cars. I walked around the car to convince myself that the sound was really coming from the car and not from some point outside the garage: I'm convinced that it was, but I couldn't confidently reach a conclusion about which part of the car it was coming from. After about 15 seconds, I opened the rear hatch and about three seconds after that, the sound stopped. Anyone have any ideas?
My guess is the car was recharging the 12V battery from the traction battery. I've seen a dashboard message about that once or twice. The noise is probably the DC-DC converter used to switch the 360V from the traction battery down to the ~14V needed to charge the little battery.
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post #3 of 10 (permalink) Old 02-27-2019, 12:57 AM Thread Starter
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I get that message about three times a week. Up until now, I've assumed it might have something to do with the fact that my alarm goes off by accident when my key fob bumps up against something in my pocket. And then it usually takes about 30 seconds for me to pull the key fob out of my pocket and shut down the horn. But whatever was humming last night sounded sounded to me like it probably sucked down more power than the horn.


You might be right about it being the converter: that message did light up the first time I drove the car after hearing this sound. But I wasn't aware that the converter would sound like a fuel pump.

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post #4 of 10 (permalink) Old 05-01-2019, 11:40 PM Thread Starter
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I heard it again tonight, under different conditions, and it's kind of disconcerting.


I went out for lunch earlier today, came back around 2 PM and parked in the garage. My EV range was down to about 10 miles. Around 6 PM, I went back to the garage and plugged in the L1 charger. There were a few of the usual clicking sounds as I plugged it in, and then a humming sound started and didn't stop. It reminded me of a fuel pump sound. It was probably about 80F in the garage and it occurred to me that it might be a battery cooling fan, so I opened the rear hatch, lifted the access panel so that I was looking at the traction battery housing, but the sound didn't seem to be coming from there. When I got down on the floor and listened from under the rear bumper, it was pretty clearly coming from somewhere under the car. I'm pretty much convinced that it was a fuel pump sound.


After a few minutes of this, I unplugged the charger from the wall, and then from the car. A moment later, the humming stopped. I reconnected the charger and the humming didn't start again.


I think it's probably been about three weeks since I last drove in a way that required the ICE to start, and I wonder if that might be a factor. It has occurred to me that it might not be good to run the ICE that infrequently. Still, if it really was a fuel pump that I heard, I'm having a hard time imagining how plugging in the charger could have triggered it to come on.


Interested to hear any ideas that people might have.

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post #5 of 10 (permalink) Old 05-02-2019, 07:16 AM
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Originally Posted by deltasmith View Post
I heard it again tonight, under different conditions, and it's kind of disconcerting.


I went out for lunch earlier today, came back around 2 PM and parked in the garage. My EV range was down to about 10 miles. Around 6 PM, I went back to the garage and plugged in the L1 charger. There were a few of the usual clicking sounds as I plugged it in, and then a humming sound started and didn't stop. It reminded me of a fuel pump sound. It was probably about 80F in the garage and it occurred to me that it might be a battery cooling fan, so I opened the rear hatch, lifted the access panel so that I was looking at the traction battery housing, but the sound didn't seem to be coming from there. When I got down on the floor and listened from under the rear bumper, it was pretty clearly coming from somewhere under the car. I'm pretty much convinced that it was a fuel pump sound.


After a few minutes of this, I unplugged the charger from the wall, and then from the car. A moment later, the humming stopped. I reconnected the charger and the humming didn't start again.


I think it's probably been about three weeks since I last drove in a way that required the ICE to start, and I wonder if that might be a factor. It has occurred to me that it might not be good to run the ICE that infrequently. Still, if it really was a fuel pump that I heard, I'm having a hard time imagining how plugging in the charger could have triggered it to come on.


Interested to hear any ideas that people might have.
I've definitely head a hum from the rear of the car when charging. My assumption was the same as yours, a cooling fan for the battery. I doubt it's the fuel pump, if the car is off, so is the ECU so it shouldn't be able to turn it on. There is a vent for the battery in the passenger cabin in the foot well of the driver's side rear seat. I assume there is a corresponding exit vent somewhere under the car and a fan to draw air through the battery. That could be the source of the sound we're hearing.

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post #6 of 10 (permalink) Old 05-02-2019, 08:06 AM
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There are definitely electronics that are powered at all times and extra ones during charging for the BMS. The key fob would not work otherwise. Humming could be coming from the two cooling fans in the PHEV during charging, but also from the inverter.

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post #7 of 10 (permalink) Old 05-02-2019, 09:43 AM
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There are definitely electronics that are powered at all times and extra ones during charging for the BMS. The key fob would not work otherwise. Humming could be coming from the two cooling fans in the PHEV during charging, but also from the inverter.
I agree that there are a lot of things powered on during charging and that many of those can be noisy but the ECU that controls the ICE shouldn't be one of them, that's the one that would run the fuel pump. That should eliminate the pump as the source of the noise deltasmith is asking about.

The noise we referring to is a specific one that only happens sometimes when charging. It's definitely localized to the rear of the vehicle, and sounds very much like a pump or fan. Do you know if there is a dedicated battery cooling fan on the PHEV? The presence of the vent in the cabin implies that there might be and that might be the sound we're hearing during charging.

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post #8 of 10 (permalink) Old 05-02-2019, 04:51 PM
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After my HEV is parked overnight, simply opening the door causes a noise coming from the engine compartment that sounds just like a fuel pump. This sound has been noted a lot on forums, but as far as I know, no one has identified the source.

One ECU does not cover all functions anymore. I think I heard someone say 17 chips in the Niro/Ioniq.

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post #9 of 10 (permalink) Old 05-02-2019, 11:54 PM Thread Starter
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Quote:
Originally Posted by yticolev View Post
After my HEV is parked overnight, simply opening the door causes a noise coming from the engine compartment that sounds just like a fuel pump. This sound has been noted a lot on forums, but as far as I know, no one has identified the source.

One ECU does not cover all functions anymore. I think I heard someone say 17 chips in the Niro/Ioniq.
I think I'm familiar with that sound, but it's different from the one I mentioned previously.

The Niro has an amazing abundance of sounds, not all of which are predictable. There is definitely a ghost in the machine. Sometimes I walk out to the car and open the door to put something inside, with no plan to actually drive the car, but as I open the door, I hear a brief hum from under the hood, as if it's anticipating that I'm about to drive. That sound only lasts for about two seconds. There are other times when I do the exact same thing and there is no hum sound.

Yes, there is a fan that is mounted on the PHEV's battery for cooling purposes, although I've never yet heard it run. But you can see the duct work for it and you can see a description of it in the online tech manual.

The sound I mentioned most recently endured for approximately two minutes and probably would have run for longer if I hadn't intervened, didn't seem to be coming from inside the car where I would have expected the battery cooling fan sound to come from, did seem to be coming from under the car, as if from a fuel-tank mounted fuel pump. I probably should have tried to make a video with audio - maybe I'll do that if it happens again.

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post #10 of 10 (permalink) Old 05-03-2019, 11:33 AM
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I believe the PHEV has two battery cooling fans, one under the rear seat, and another under the load floor in back.

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