I have a MacBook Air 2013, which randomly started having issues with the fan speed shooting up (from booting and no applications running) and just completely slowing down. Apple said it was a problem with the SMC controller and logic board. I have reset the SMC 10 times and wiped the laptop. Finally, I have downloaded TG Pro which has solved the fan issue but the Kernel task is still eating up CPU even though the CPU temp is around 45 degrees. Any clues?

CPU PECI 46 degrees.

Activity Monitor: kernel_task 258.1% CPU

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    If you are measuring the temperatures after kernel_task has things throttled, how can you be sure the problem isn’t the control circuitry and sensors? I would trust Apple on the diagnosis tbh, but maybe you have some more details to share?
    – bmike
    Commented Mar 20, 2021 at 12:39
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    Does this answer your question? Why is kernel_task using so much CPU?
    – IconDaemon
    Commented Mar 20, 2021 at 12:41
  • Hi Bmike I have added the data TG pro showing the temps. My background is all mechanical so I apologise if that is not what you was looking for
    – Derek
    Commented Mar 20, 2021 at 18:13
  • What are the temperatures when kernel task uses less than 5% ? (And note, the software used to measure stats is known to cause high kernel usage)
    – bmike
    Commented Mar 20, 2021 at 18:55

1 Answer 1


All signs point to your system that measures temperature is out of spec or failing/failed. It’s also likely software is piling on, adding legitimate load to the kernel, making the issue worse.

One SMC reset a month is too often to cure any physical defect. Second and third resets too quickly won’t help you.

A single SMC reset cures a wrong state measurement if that’s the cause of an issue. You won’t have to do that again for months on functional hardware in my experience.

Sadly, the cost to diagnose and fix a main board is high so most people do the swap as Apple recommended if you can’t live with the system design to let kernel task protect the system.

Too high CPU is a judgement / budgetary call on how much you value your time and not so much a technical issue.

The system does what it’s designed to do based on measurements. Worse, installing software to track temperature moment to moment can put enough load on a system to cause CPU spikes and add legitimate work kernel_task now has to perform while its stalling - simply observing the system can change it. You might have to remove all modifications to tell if your software is the cause here.

To test a clean system you need a cheap USB drive that holds 32 GB and network that can download about 15 GB of data from Apple. You can do the test faster with fast internet and speedy external storage, but a weekend and cheap parts, slow internet is all that’s needed to run a clean new OS to validate your SMC and kernel_task isn’t a software issue.

  • thank you BMike. I maybe over simplifying this so please correct me if I am wrong from what I can see the TGpro the most of the systems that temperatures seem to be fine but not all that is physical defect is causing the kernel task push CPU so that CPU can come back down to a safe temp. I don't plan to use MBA for anything more light web browsing with the occasional video call & not for very long too is there a way to stop the Kernal task?
    – Derek
    Commented Mar 20, 2021 at 18:05
  • I don’t think you’re wrong at all, just suspect you are out of easy options @Derek
    – bmike
    Commented Mar 20, 2021 at 18:08
  • fair enough, I unfortunately in the immediate future this is my only machine, I have time and tools not so much on the money side as you can imagine is there anything you recommend. I have engineering background so I would be okay taking the machine apart but I imagine there is more to the story
    – Derek
    Commented Mar 20, 2021 at 18:20
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    Good plan @Derek it might be interesting if you have an external drive to install a clean macOS and set the Mac system preferences to boot from that clean OS. Install nothing, no temp software, sign in to no cloud accounts. Literally install the OS to make an account you can let run for 2 hours and then see how low kernel_task it can run at idle. Disconnected from the internet after you make your account, totally clean system.
    – bmike
    Commented Mar 20, 2021 at 19:00

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