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


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...

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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.