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Released on October 23, 2012. Core i5 or Core i7 Processor. Apple Fusion Drive.

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Fan full speed and CPU 100% (probably not actually high temps)

Hello – I have a late 2012 Mac Mini. It has been perfectly reliable since purchase new. I woke up this morning to the fan at full speed and the system effectively unresponsive. The processor was pegged at 100% utilization, with the “kernel_task” process being the culprit. My understanding is that “kernel_task” is used to steal CPU cycles to help prevent thermal issues and reduce temperature.

I figured something crashed / a process got out of control and powered it off. Upon restarting the Mac Mini, the fan resumed full speed immediately. Even before I was prompted to enter my password for FileVault.

If I go into Recovery mode (CMD + R at boot) the fan is maxed and system is crazy slow. I installed Macs Fan Control app and it reports that the fan is maxed RPM wise (approx. 5,000) and ALL temps are reporting to be very cool (approx. 43C / 110F).

This tells me that the CPU is not actually pegged (not hot). Which also aligns in that it the fan is full speed no matter what. Even pulled hard drive (Samsung EVO SSD) out and turned on, fan went to full speed.

No dust inside, super clean. Reseated memory. Reset SMC and NVRAM/PRAM. Even replaced PRAM batter.

Not sure what else to do and fear this is simply a hardware failure of sort. Just odd that it still boots up and functions, be it ever so incredibly slowly as the CPU is limp mode of sort.

Wonder what is feeding it (in theory) bad info causing fan to max out and CPU to be limited. I would guess bad temp sensor but didn’t see anything to indicate that in Macs Fan Control.

Nothing has changed hardware or software with it in a while. Simply idling on desk happily until this morning. Any thoughts / help would be greatly appreciated!!!

Update (09/18/2019)

Here is the fan speed and sensor temps. Looks like things are really cool and CPU is really idling, even though it is in "limp mode" of sort. Took 20 minutes to boot up and me to down/install/run the app because all CPU cycles are being stolen by "kernel_task" process.

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You'll need to run the onboard diagnostics to see if you get an error message. Restart the system and this time hold the D key. Let us know if you get an error message.

Reference: Mac startup key combinations

MacsFanControl won't report the voltage sensors which can also set off SMC.

What you are seeing is SMC pushing the system in to Safe Mode ramping up the Fan and slowing down the CPU so its not running hot.

Until you can identify the error its tough to tell you what will be needed.

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Shoot, forgot to mention. I cannot get it to boot into diagnostics just pressing D at boot.

Per you link, I just tried Option + D which started to work but error'd out with:

"Error:0x8000000000000003, Cannot Load 'EFI/Drivers/TestSupport.efi'

Status: 0x00000003"

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Thanks to Apple ;-{{ !!

Any luck with SMC reset?

Reference: How to reset the System Management Controller (SMC) on your Mac

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At this point you’ll need to visit an Apple Store as they will run the in-house diagnostics (for free) and make sure they tell you what it showed. You don’t need to leave it for them to fix just give us the code that pops. Then we can see what your options are.

Update

OK so we can see clearly the thermals are not pushing the fan. So there is only two things here either the logic board voltage sensors are failing which I was thinking at the start and going to the Apple Store to check the diagnostics didn’t pop an error (it should have) so that only leaves a bad fan or the connection to the logic board is damaged so the tach logic is not communicating to SMC.

Follow this guide Mac mini Late 2012 Fan Replacement taking the fan out make sure the connection to the logic board is not damaged as well as the wires are not pinched. You may want to just replace the fan Intel Mac mini (A1347 Mid 2011-Late 2014) Fan. Hopefully that fixes it! If you see any damage take a good pic and post it here for us to see the damage.

Intel Mac mini (A1347 Mid 2011-Late 2014) Fan Imagem

Product

Intel Mac mini (A1347 Mid 2011-Late 2014) Fan

$54,99

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No luck with SMC reset. This was done multiple times, especially when I replaced NVRAM battery.

Don't have much hope here .... still odd that it boots and "works" ... sorta.

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@yerod - SMC measures more than just temps it also tests voltages. While you may have proved the issue was not a thermal issue, we can't isolate out what is happing with the voltage sensors as we can't get diagnostics running.

The code it offers give us the clue where to look. You may need a new logic board at worse. Sometimes we can fix the logic board.

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I have Genius Bar appoitment for tomorrow afternoon. We shall see. I'm sure it will result with a "needs new logic board for $400+"

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@yerod - Make sure you get the diagnostic codes! Write them down and let us know!

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Soooo ... Apple Genius tech ran all sorts and there were no errors. Their tools came up with nothing. Even booted into their diag version of Mojave where the issue repeated itself.

Forgot to mention above, but I also changed out memory just for giggles with no improvement.

Tech said I could bring back and leave for couple days for extended testing but said probably logic board (shocker, it's Apple's favorite move) and would be $350. Not sure I am willing to invest that into the 2012 Mini. Sigh ...

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Unlikely, but you may want to open the thing up and check for dust and stuff in the fans, making the fan read incorrectly. I believe that there is also a fan controller app for macs that you can install to regulate your fans on the fly. Other than that, I would recommend running ASD (Apple Service Diagnostics) on it and seeing what it comes back with. Worse comes to worst, you could always take it into an independent repair shop nearby and see what their take on it is. (Use the Apple Store as a last result; they’ll make you pay 20x more for what actually needs to be done) :)

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