High CPU usage kernel_task with 2 monitors

Hello guys!

Anyone out there with high CPU usage issues by kernel_task when you have two monitors connected by Thunderbolt? CPU usage at 1300%. I have to shut down one monitor.

Have tested all the betas and the GM and nothing. In Yosemite works quiet.

My setup;

MacBookPro 15 Retina 2012

2.3 Core i7


2 monitors LG

Post not yet marked as solved Up vote post of Junqueira Down vote post of Junqueira
  • For whom having external monitors, like I have 2, we also have to make sure external monitors are in good operating temperature too. My symptom was my Mac book was working great in the morning, but began to have this issue in the afternoon. This issue showed up very consistently after entering into summer here. Finally, my solution is to have one fan to cool down my external monitors so that I can continue my work in the afternoon without any problem now. Hope this can help people similar to my.

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Hi Junqueira,

The following should fix the high kernel_task CPU usage:

  1. Disconnect both external monitors.
  2. Shut down the Mac.
  3. Plug in the MagSafe power adapter to a power source and to your Mac.
  4. On the built-in keyboard, press the (left side) Shift+Control+Option keys and the power button at the same time.
  5. Release all the keys and the power button at the same time to reset the SMC.
  6. Press the power button to turn on the computer.
  7. After fully booting into OS X, shut down again.
  8. Press and hold the Command+Option+P+R keys immediately after you hear the startup sound.
  9. Hold these keys until the computer restarts and you hear the startup sound for a second time for the NVRAM reset.
  10. Release the keys and log in as usual.
  11. Reconnect your external displays and keep an eye on the CPU usage.

Let us know if this fixes it for you...


  • Can't believe after digging around the entire internet, this comment saved my macbook (2019 16inch). After doing the reset SMC and reset NVRAM, I have not seen the kernel_task clogging up issue anymore

  • Update: the problem is back, reset SMC and NVRAM did not resolve the kernel_task issue...

  • the above 'fix' does not change anything. still kernel task is over 500%. this is a pretty big letdown by apple :(

Confirmed this help.

I was facing this problem a lot.My CPU usage would reach above 1000 percent and most of it would be by Kernel_task. Whenever we connect second display or use heavy applications ,it requires more gpu/cpu power so our computer heats up more. If the temperature rises too high, Mac Os will run a dummy process "Kernel_task" to reserve cpu usage but keep it idle to reduce load of cpu and protect the computer from burning. As the temperature lowers it will release the resources. The problem in my case was accumulation of dust in the CPU and GPU fan.It had probably sucked it through the side vents. I cleaned it and it works like breeze. I even changed the thermal paste on my CPU and GPU as it had become hard over time and excessive heating. Hope this helps.

  • Thanks @RobbySingh ! I had the same issue until last week - when I saw this comment and decided to clean up the fans. They were really dirty - full of dust (large chunks!). No wonder that they never were able to spin at full capacity - that also explains why lately I have been having other issues. Thanks for the hint, that was really good!

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Hello @RobbySingh, I suspect it might be the case with me as well. How did you get your CPU and GPU fan cleaned? Did you have to unscrew and open up your Mac Book?

@joeltom21, yes you need to open up your case. But, if you are in US, you can make a Genius Bar appointment at apple store and ask them to open you laptop and clean the fans. They don't charge for this and very safe way to do it as they have appropriate pentalobe screwdriver etc. I had exact same issue with with my MBP, where connecting external monitors would make a 2019 model useless duet o kernel_task cpu usage. When I got the fans cleaned at Apple store, my MacBook was back in game. I am now able to connect two monitors with no issues whatsoever. My MBP runs without any noise where as earlier it used to due to the dust trapped in fans reducing their cooling efficiency.

  • @santoshm thank you so much!!! This was my solution finally!!! I have a macbookPro 2019 16'' and "Kernel_task" get to the roof (700%) when connected to external monitor! Then I read this comment, made a Genius Bar appointment at apple store, my fans got clean (for free), they had accumulated a lot of dust, and now everything is back to normal! so happy!

  • This solved it for me also!

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I was having this problem recently also. Depending on what year your Macbook Pro is... if you have the power (charging) cable plugged into the left side. I would recommend first trying to move the power to the right side of your laptop. This is apparently a known issue with 2019 MBP's especially with the 16 inch model. Also, I found that because i had purchased a magnetic adapter online for my power cable, when i removed it, the high kenel task magically disappeared. Id recommend trying the same!

  • I can't believe it worked. I move the power cable to the right side and the kernel_task process stopped hogging my cpu, at least for now it's only sitting at around 5% instead of 700%. This is so dumb... Anyway thank you so much JustinH2O

  • I also have the MBP 2019 and I tried this, moving the power connection to the right side and I have both monitors now on the left. I instantly saw the kernal_task drop from over 700 to just 5! Problem solved so far. I did not try any of the other solutions, I didn't even reboot. Thanks.

  • CRAZY bug. I was struggling for long time about using monitors.. When I plugged into right side monitor cable, my CPU goes to 95% usage. I found this thread and tried to switch power cable to right side and monitor cable to left side and my CPU is now at 12%.

    OMG, I stayed long time without using second monitor due to this issue. So cool!! Thank you @JustinH2O.

Do we have any solution for this issue? I’ve been running into the exact same thing with my external monitor connected. Resetting the SMC only helps temporarily but the issue returns after sometime. I have to consistently disconnect my external monitor in order to restore the CPU (kernel_task) spin and then reconnect.

There ought to be a solution out there for this. I’m really hoping Apple support can step in to help with this.

  • Your Mac is most likely overheating. This can happen even if your core temperature seems normal as the OS steps in preemptively to cool things down. That’s the kernel_task spiking as it does dummy processes to spare your cpu. I recently had my fans cleaned, new thermal grease applied and a swollen battery replaced by Apple technicians and now I can use my Apple Cinema Display again - and overall performance much better.

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I have the same issue - but only since I upgraded to MacOS Monterrey :( - I need to work with an additional external monitor and especially with the current heat wave it's not possible - I even bought a cooling pad with 5 fans - still the issue persists :(

  • Same here. Problem suddenly appeared after a routine OS Monterey update. Tried all the suggested solutions with no luck. Desperate :-/

    2015 MacBook Pro retina 16gb ram 2TB SSD External monitor connected thru HDMI (disconnecting did not help)

  • do you think it is related to Montery OS? I am also having the same issues

  • Same issue after upgraded to MacOS Monterrey

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Same happen to my Macbook Pro 15" 2017 and it seems this issue started after upgrade to MacOS Monterey. It caused the whole laptop freeze and unusable. Can't believe such a premium laptop have this kind of problem! I even formatted my harddisk and reinstalled the Monterey but the issue still persists! Resetting the SMC did not help but disconnecting the monitor immediately see kernel_task dropped. Reconnecting back the monitor will not immediately trigger the problem but after awhile the problem came back.

Hi, I am also am having the same issues and had to disconnect the second monitor. I tried all sort of combination to see if the kernel_task reduces the load but no luck. only when I disconnect the second monitor it seems it goes back to normal. I haven't tried to clean and re paste the CPU and the fans but when I look at the fans it is very clean. not sure if this really an issue. I also run the Macs fan control app to control the fan speed and the temp but I think this is not related to the issue. I also tried the SMC reset and NVRAM etc., but last only few minutes and its back again.... I am very frustrated.. I am running Montery on my mid 2015 MBP... any help really would be appreciated. thanks

  • You should also look at replacing thermal grease and new battery if it’s a MacBook. This solved the problem for me. Hope this helps.

  • this is exactly what is happening to mine 2015 macbook pro 15inch also. I only have not tried to repaste the cpu as the fan and board and they look still very clean.. It is really frustrating and hope apple or someone really can solve this issue. I think this is a design flaw from apple.

  • I have repasted the CPU, GPU and cleaned again the fans.. still the same... it is really frustrating and I am thinking selling and get rid of macbook..!!

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Same issue with my 2016 Macbook Pro 15". It was a dual monitor setup, one being a super ultra wide and one regular. No issues whatsoever until all of the sudden it was slower than molasses. Turns out my MacBook was extremely hot (In clamshell mode) even though I'm running fans at full blasts and CPU only reads 50-62 degrees Celsius. Opened the laptop for about minute and it cooled down immediately and kernal usage dropped like a brick on the CPU. My system CPU usage went from 85% to 5% after the laptop cooled down while being open. I read one response on here regarding the charging thunderbolt cable being on the left side, so I've switched to the right to check on how it would handle clamshell mode now. For now it seems fine, though I'm sure that may change here in a couple hours. Respond here and I'll try to report back with an update.

Having the same issue here. I use a dual monitor setup both at home and at work. Funny thing is that it seems only to happen at home. The temperature in both places is around the same. I have in both cases a ultra wide 4K 38" Monitor. At home I connect it through USB-C, the problem seems to disappear shortly after I disconnect the dual screen or reboot the mac. However at work, I don't seem to have the issue, and it is conneced with a display port with an adapter to USB-C

the only way to solve this issue, especially after updating your OS, is by connecting external display/s through HDMI adapter, instade of USB-C.

its working like a charm.

Shame on you Apple.. updating is slowing down your macbook, so you think you need to buy the new one.

Hi Modimoni, thank you for this feedback. I'm in the same trouble, I cannot plug anymore my two screens, it makes my Kernel_Task goes super high, it's super frustrating. The problem I have is my screens doesn't have HDMI plug, they only have USB-C plug. It's LG ULTRAFINE DISPLAY 27". Do you have any suggestions to help ? Many thanks.

  • Same issue and same setup here. I have no permanent solution. Currently, I use an external fan (powerful) to cool the MacBook and it solve the problem. However, I also pan to use my Macbook in the classroom to teach, which is really inconvenient to bring a huge fan with me:( I am very disappointment with Apple. This issue can not be solved by reset SMC or NVRAM.

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I see so many same issue on this topic and it seems there is really no solution as I have tried every single possible things recommended and suggested in the internet..! I think this is a design flaw either software/maybe also hardware by Apple on this models. Apple really should give their position and fix on this..!