Extremely High kernel_task (usually range 400-1400%)

Then I noticed that kernel_task is extremely high and based on some forum information, I replaced the HDD to SSD and reapplied thermal paste.

The reason is almost certain to be a disconnected thermal sensor used to monitor hard disk drive temperature. It absolutely, positively must be present.

When replacing a hard disk drive with a SSD, an appropriate adapter or connector is required or the Mac will conclude the hard disk drive is overheating and will throttle its CPU and operate its exhaust fans at maximum speed, in a futile attempt to keep it cool.

Please read If kernel_task is using a large percentage of your Mac CPU - Apple Support.

A runaway kernel_task can be due to a number of factors, such as:

• a failed or disconnected temperature sensor
• cooling system inefficiency (an inoperative exhaust fan on Macs so equipped, possibly clogged with dust, including the heat sink)
• a worn out, missing, or non-Apple (user-installed) battery on portable Macs
• similar hardware-specific causes including internal hardware additions or modifications, external USB and other connected devices, or the driver software required to use them.

If you can find no other explanation for its behavior, an SMC Reset is justified: Reset the System Management Controller (SMC) on your Mac - Apple Support.

To post the EtreCheck report in a reply to this Discussion, refer to Old Toad's spectacular User Tip, here:

How to use the Add Text Feature When Posting Large Amounts of Text, i.e. an Etrecheck Report - Apple Community

Of course it is not possible to determine the reason kernel_task was excessive prior to replacing the HDD, but a hard disk in a Mac of that age was likely to be operating in a state of failure anyway. Replacing it was a good idea, and it should work, but I am not familiar with the OSC SSD. The only SSDs I have used and can comfortably recommend are sold by OWC / MacSales, and I do not know if they can deliver to Sri Lanka.

On that subject, given Sri Lanka's present state of affairs it will be difficult to obtain anything by way of in-person assistance, but another option could be to obtain an external Thunderbolt-connected SSD and use it in lieu of the internal one. Its performance should be equal to that of an internal SSD, but the question of a thermal sensor still needs to be addressed.

At the time that EtreCheck report was generated, the CPU was not overly burdened — the total opposite of your original screenshot, which revealed it had almost no idle time. A Mac will be almost totally unresponsive in that condition. Unfortunately the information we have remains inconclusive, but in an effort to advance troubleshooting consider using Apple Hardware Test. It may or may not reveal any actionable information.

I would not be concerned about JMicronATA.kext. It is installed by default by macOS. It should be present, even though it may not be in use. I don't believe it is contributing to the problem.

Anyway, I am not an EtreCheck expert, but I will attempt to attract the attention of its developer and ask him to help you.

The JMicron driver may be part of some third party software that you installed since it is shown in the EtreCheck report. If so, then it is possible it may cause a problem.

According to OWC there is no need for a thermal sensor adapter for the 21.5" 2012 iMac (there is no thermal sensor adapter included with their SSD upgrade kit, nor does the installation video mention it).

However, one of the other contributors recently mentioned that a High kernel_task can be due to macOS thinking the system is overheating and uses the high kernel_task as a way to "idle" the system in order to allow it to cool down. I've never really noticed this behavior before, but I also never knew to look for it. When I have performed system stress tests on Apple laptops to test their cooling systems, I have observed they will throttle the CPU speed once the fans are running at maximum speed. Perhaps the kernel_task was used with older version of macOS and older CPU models instead since the later CPUs will thermal throttle to protect themselves.

I also never heard of OCS SSD so I don't know how they work or their quality. Many SSDs today are very low end models which have performance issues. I agree with @John Galt that your old hard drive was most likely failing and causing problems, but I don't know whether this SSD is even compatible with this Mac. Unfortunately not all SSDs are compatible with all computers. Booting from an external USB3 SSD is a good way of testing this iMac, but you will either need to install a thermal sensor adapter or reinstall the original Apple hard drive so that the iMac has a working drive temperature sensor. If you reinstall the original Apple hard drive, then you could run DriveDx to check the health of the hard drive so we can see whether the hard drive is bad. Running EtreCheck while booted to your original hard drive could also tell us whether you may also have had any software issues contributing to the problem.

Another SSD option is the Crucial MX500 series SSD. I have used them in our organization's Macs without any issues. However, stay away from the Crucial BX500 series as it is a low end model that can be as slow as a hard drive and tends to overheat very easily when writing lots of data. Plus the BX500 SSDs tend to have an extremely high failure rate.

Don't be surprised if the Apple Diagnostics report a drive failure while your new SSD is installed. If the new SSD does not respond to the diagnostics as expected, then it will be reported as a failure even if the SSD is perfectly fine & healthy. Also, since you have Catalina installed you may have access to the online Apple Diagnostics (hard to tell since some system firmware updates break access to both the online Apple Diagnostics and the older Apple Hardware Test mentioned by @John Galt.

Since you only have the JMicron driver installed and the userland portion of One Drive, the only thing I can think of is whether One Drive is even fully installed and could be the cause of the problem. I don't use the OneDrive app so I'm not certain if it requires any other lower level system integration.

The best thing you can do would be to install the thermal sensor adapter and if you still have the problem, then perform a clean install of macOS by erasing the whole physical SSD before re-installing macOS. Then test the system before you install any third party software and before restoring/migrating from a backup. If you still have the problem with a clean install under these conditions, then you have a hardware issue with the iMac. The OCS SSD could be the problem so testing a clean install from an external USB3 SSD would help to eliminate the OCS SSD as part of the problem. Now you could try the clean install even without the thermal sensor adapter, but the results of the test would be inconclusive if you still have the problem.

I think these are your best options if you cannot have Apple or an AASP examine the iMac.

To look for possible software issues run EtreCheck and give EtreCheck "Full Disk Access" so the report includes more details which may provide more clues for us to help you. Post the report here using the "Additional Text" icon which looks like a piece of paper.

ranjithwp wrote:

Etrecheck report also suggest problem of JMicronATA.kext.

EtreCheck is just warning you that Apple is in the process of discontinuing support for kernel extensions. If you had some kind of hardware that required this extension, then you could lose access to the hardware at some point in the future.

There have been a number of situations recently where Apple discontinued certain older hardware or older types of software and many end users had no idea until they upgraded their system and lost access to some hardware device or software. EtreCheck is just trying to warn you about that possibility ahead of time.

However, EtreCheck doesn't examine in detail what the extension does or whether or not you really need it. As far as I can tell, you aren't using this kernel extension anyway.

The OCS SSD would be my prime suspect since the EtreCheck report does not show any software that may cause the problem. The speed of that SSD while slightly better in the most recent EtreCheck report is still dreadfully slow. Everything you have posted here would have me replace the OCS SSD with a respected name brand SSD such as the Crucial MX500 SSD, or an OWC Mercury Electra 6G SSD are the safest options. The Samsung EVO 860 SSD, or even a WD or SanDisk SSD would be much better options than the unknown OCS SSD you are currently using. Certainly one of these are available in your region.

I'm fairly certain the original hard drive was failing and was the source of the original problem. A macOS install puts a lot of stress on an old hard drive and will usually reveal latent issues. Plus you are still experiencing similar issues with an unknown brand of SSD which is proven to have very poor performance as shown in the EtreCheck report. So your iMac has had two slow drives which have produced the same poor behavior. Seems like the SSD is the best & most likely place to start. If it is not the SSD, then like @etresoft mentions, it probably isn't worth spending any more money on this old iMac. This iMac is considered "Obsolete" by Apple so you won't be able to get any official repair by Apple and macOS Catalina is the last supported version of macOS for this iMac which will stop receiving security updates later this year (Catalina is already missing out on some security updates as it is anyway). At least a good SSD can be repurposed to any other computer so you won't be losing any money the SSD unlike any other component which is specific to this Mac.

That kernel extension is not causing this problem. The computer is 10 years old. You need to buy a new one.