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User profile for user: mkulaksiz
mkulaksiz Author
User level: Level 1
4 points

Kernel_Task high CPU Usage since new SSD installed

Hi all,


My iMac (Retina 5K, 27-inch, Late 2014 - Spec) is running exceptionally slow, having just had a local IT repair shop replace the original Fusion Drive with a 1TB SATA SSD. I have then restored the iMac from a backup.


(I don't have the time/opportunity to just take it back to the IT shop, and as the solution shouldn't need to involve opening it up - I know the inside is clean - I'd like to do it myself)


Having investigated the cause, everything points to an exceptionally high Kernel_Task usage - current snapshot of activity monitor:



The closest Mac forum thread I have found to this is: 8337838


I'm not sure if it is associated, but one issue not anticipated when the IT shop replaced the HDD was that the fan controller for this model was built in to the Apple Fusion HDD, so the only workaround was to install a third party software (Macs Fan Control) to control the fan speed. References I've found to resolving issues with a runaway kernel task (incl. the forum link above) state that a failed or disconnected temperature sensor could be a cause; however, the temp sensors appear to be working fine, as confirmed by the Macs Fan Speed app:



I've restarted the machine, cleared the cache, don't have many third party software and only the Mac fan controller on my startup list.


Can anyone offer solutions (preferably not involving removing the SSD and going back to the old one) I'm sure others must have installed non-apple SSDs?... I hope...


Many thanks in advance!


Dave's To Question My Question

iMac 21.5", macOS 10.15

Posted on Dec 12, 2019 3:37 AM

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User profile for user: chris_g1
chris_g1
User level: Community Specialist

Dec 16, 2019 10:03 AM in response to mkulaksiz

Hi mkulaksiz,


Thanks for posting. As I understand it, your Mac shows high kernel_task usage after having a hard drive replacement performed. This link is a great reference point for behavior like this: If kernel_task is using a large percentage of your Mac CPU


From your description, it sounds very likely that the fan controller issue you mentioned is the cause. This resource has some information about third-party fan management and temperature monitoring apps for reference: Keep your Mac notebook within acceptable operating temperatures


As a test, it might be worth seeing if it's possible to reset your System Management Controller: How to reset the System Management Controller (SMC) on your Mac


If that doesn't help, your best bet is to get back in touch with the technician who performed the repair since this behavior sounds likely to relate to the issue that came up during the repair.


Take care.

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Kernel_Task high CPU Usage since new SSD installed

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