Resolved 2020 27" iMac fan suddenly goes full throttle for a few minutes (about once a day)

[RoboCop001]

I've only checked the the TG Pro report, in which the fan was spinning 2700 RPM. Is there another fan speed report you had in mind?

I use Macs Fan Control, but I would imagine it will show you the same thing.

Hmm... my issue was that when it happened, it reported 0 RPMs, which meant some kind of hardware issue. Probably as a failsafe, if it's reading 0 RPMs then it tells the fan to go maximum speed. Which actually went beyond 2700 RPMs and into 3000s.

Yours might just be something strange software-wise.

 

[Brachaci]

I use Macs Fan Control, but I would imagine it will show you the same thing.

Hmm... my issue was that when it happened, it reported 0 RPMs, which meant some kind of hardware issue. Probably as a failsafe, if it's reading 0 RPMs then it tells the fan to go maximum speed. Which actually went beyond 2700 RPMs and into 3000s.

Yours might just be something strange software-wise.

Most likely, but I’ll check and see if that shows any difference.

I’m hoping it will be solved by next software update though.

 

[RoboCop001]

Most likely, but I’ll check and see if that shows any difference.

I’m hoping it will be solved by next software update though.

Hopefully that fixes it for you. Keep us updated. How often is it happening now?

 

[Brachaci]

Hopefully that fixes it for you. Keep us updated. How often is it happening now?

I have checked both reports and the output is consistent

 

[RoboCop001]

I have checked both reports and the output is consistent

Does the fan go high when you're not doing anything on the computer? And if so, is CPU usage relatively idle during the high fan speed? Or is usage peaking?

 

[Brachaci]

Does the fan go high when you're not doing anything on the computer? And if so, is CPU usage relatively idle during the high fan speed? Or is usage peaking?

Yes, it is going high when the computer is asleep. When I wake it up it is still running fans. The CPU is idle, but I haven't displayed all processes in the activity monitor, so I may have overlooked something. I will post it here when the issue will get back again.

 

[RoboCop001]

Yes, it is going high when the computer is asleep. When I wake it up it is still running fans. The CPU is idle, but I haven't displayed all processes in the activity monitor, so I may have overlooked something. I will post it here when the issue will get back again.

Sounds good. I suppose one way you could test it out (before the next macOS update) is to create an external boot drive with a fresh install of macOS and leave it on for a day and see what happens.

 

[Brachaci]

I have gathered TG Pro logs from early December and can say that the last time when I saw in the report the RPM spinning high was the day when the 12.1 was released. After the update I haven't noticed anything out the ordinary.

 

[RoboCop001]

I have gathered TG Pro logs from early December and can say that the last time when I saw in the report the RPM spinning high was the day when the 12.1 was released. After the update I haven't noticed anything out the ordinary.

Nice! Hopefully that's it then.

 

[Vinyldust]

Just adding a bit of an update here ... I've been having this issue with my 2020 BTO iMac.

It's been to 2 apple stores now to try and solve - the fan can fire for days, then go back to acting normal for a couple days before fans acting up - I've found that when the fan fires, the iMac will deploy a PF0003 AND PF0004 fan issue codes in the Diagnostic window - but when I brought to apple, it didn't reproduce.

I suspect this will lead to a logic board replacement as well, but will let everyone know. (it's back at an AASP as we speak for another round of diagnostics)

One thing to note, this reproduced even after completely erasing hard drive and re-installing OSX.

Though I'd mention the Diagnostic codes in case anyone has seen them in their troubleshooting.

 

[Brachaci]

Just adding a bit of an update here ... I've been having this issue with my 2020 BTO iMac.

It's been to 2 apple stores now to try and solve - the fan can fire for days, then go back to acting normal for a couple days before fans acting up - I've found that when the fan fires, the iMac will deploy a PF0003 AND PF0004 fan issue codes in the Diagnostic window - but when I brought to apple, it didn't reproduce.

I suspect this will lead to a logic board replacement as well, but will let everyone know. (it's back at an AASP as we speak for another round of diagnostics)

One thing to note, this reproduced even after completely erasing hard drive and re-installing OSX.

Though I'd mention the Diagnostic codes in case anyone has seen them in their troubleshooting.

What do you mean "fire for days"? Is it constantly spinning in high RPM for that long? I was experiencing only short bursts of high RPM. Around 1 minute and then it suddenly went quiet. Although the issue seems to be not occuring, at least not when I am around the iMac, but I still see in the TG Pro app window that Main Fan may not be working properly.

 

[RoboCop001]

Just adding a bit of an update here ... I've been having this issue with my 2020 BTO iMac.

It's been to 2 apple stores now to try and solve - the fan can fire for days, then go back to acting normal for a couple days before fans acting up - I've found that when the fan fires, the iMac will deploy a PF0003 AND PF0004 fan issue codes in the Diagnostic window - but when I brought to apple, it didn't reproduce.

I suspect this will lead to a logic board replacement as well, but will let everyone know. (it's back at an AASP as we speak for another round of diagnostics)

One thing to note, this reproduced even after completely erasing hard drive and re-installing OSX.

Though I'd mention the Diagnostic codes in case anyone has seen them in their troubleshooting.

Is your machine still under warranty/AppleCare? If they can't figure it out, I would ask them if they can either replace the fan or the whole board. That's what they did with mine.

 

[BritishB0xer]

Update 4
It kept happening. I took it to an authorized repair place and they couldn’t figure it out. So they replaced the whole logic board. Now it works fine. So it must’ve been some kind of hardware defect. I’m guessing a faulty sensor.

What OS are you using?
Certain updates and upgrades cancel out support for GPU which causes over heating...iw as told this because my iMac screen goes black yet it works in safe mode.

Try safe mode to see if it was an Apple update.

 

[RoboCop001]

What OS are you using?
Certain updates and upgrades cancel out support for GPU which causes over heating...iw as told this because my iMac screen goes black yet it works in safe mode.

Try safe mode to see if it was an Apple update.

It would still do it in safe mode actually. It began happening before Big Sur was released, and continued to happen after I updated to Big Sur as well.

But ever since they replaced the logic board it's been fine. Plus, whenever it would be going high speed the RPMs would read as zero. So both the technician and I were thinking it was some kind of hardware fault, but couldn't figure out what it was.

 

[BritishB0xer]

It would still do it in safe mode actually. It began happening before Big Sur was released, and continued to happen after I updated to Big Sur as well.

But ever since they replaced the logic board it's been fine. Plus, whenever it would be going high speed the RPMs would read as zero. So both the technician and I were thinking it was some kind of hardware fault, but couldn't figure out what it was.

firmware and 3rd party drivers are actually not the same, i personally think that if Apple has so much control they should be renting their computers and deal with the problems themselves, dont be surprised if there no isues for decades.

im sorry if i did not read entirely through this thread so incase i missed it i like to ask you how much did the logic board and all cost you?

 

[RoboCop001]

firmware and 3rd party drivers are actually not the same, i personally think that if Apple has so much control they should be renting their computers and deal with the problems themselves, dont be surprised if there no isues for decades.

im sorry if i did not read entirely through this thread so incase i missed it i like to ask you how much did the logic board and all cost you?

It was free because it began happening about a month after I bought it lol. I basically got it when they were announced in 2020. It was fine for a bit, then just started happening one day. I can't remember if there was an OS update, but I didn't install anything new at that point in terms of software.

No worries for not reading the whole thread. All of my important details are in the first post in all of the updates. I pretty much did all the things I could think of. Reset PRAM. Ran it in safe mode for a while.

When they replaced the logic board, they just brought over the SSD so everything was identical in terms of software. Now it's running just fine. I have a feeling the fan's RPM sensor was somehow faulty. The reason they didn't just replace the fan was because they weren't completely sure it was a fan fault or somewhere else on the board. So the technician figured, just replace the whole thing.

 

[BritishB0xer]

The reason they didn't just replace the fan was because they weren't completely sure it was a fan fault or somewhere else on the board. So the technician figured, just replace the whole thing.

it would be very interesting to discover if this fan was the cause of the previous issues

 

[RoboCop001]

it would be very interesting to discover if this fan was the cause of the previous issues

Yeah I would've liked to have known what the problem was as well. I think it was likely just the fan component and a bad RPM sensor. Since it was reporting 0 RPMs during these moments, I figure as a failsafe it would just tell the fan to go maximum speed to ensure the computer gets cooled.

 

[Vinyldust]

Is your machine still under warranty/AppleCare? If they can't figure it out, I would ask them if they can either replace the fan or the whole board. That's what they did with mine.

So, the machine is technically out of warranty - It was purchased on launch in august 2020 - but since my last update - I can confirm - an AASP opened up the iMac, and the fan did finally fire, and they see the weird activity - they took a few more days to see if it was the fan, or the logic board that was causing the issue - but had an issue pin pointing. They suggested replacing logic board and fan.

I called apple and they agreed to create an exception on this given all my tickets about the fan, and did give the green light to the AASP to replace the logic board and the fan - I hope to be able to pick the repaired computer up at the end of this week assuming parts arrive on time tomorrow. (It was a BTO logic board ).

Hope this will solve all the issues !

 

[Vinyldust]

it would be very interesting to discover if this fan was the cause of the previous issues

Just to add a bit of colour per my post above - AASP that I brought mine to had a tough time seeing where/what was triggering the fan - they've opted to replace both the board and fan. Would prefer to know if it was one or the other, and ultimately, hope it won't be reproduced once they replace both parts ... but seems like there's a point where it's not worth tracing it anymore and just opting for the replacement part...

 

[RoboCop001]

Just to add a bit of colour per my post above - AASP that I brought mine to had a tough time seeing where/what was triggering the fan - they've opted to replace both the board and fan. Would prefer to know if it was one or the other, and ultimately, hope it won't be reproduced once they replace both parts ... but seems like there's a point where it's not worth tracing it anymore and just opting for the replacement part...

Sounds exactly like what happened with me! Mine is BTO as well. The problem must be something really small and easily missed. I'm glad they still repaired it for free for you. That must've been a bit of relief.

 

[Rickbot]

Same fan problem, refurb 2020 27" 3.8 GHz 8-Core Intel Core i7 iMac. 3 visits to Apple store and no answer. one SSD wipe and OS re-install to Monterey 12.4. Fan would speed to 3600 rpm, usually on wake-up, with no apps running. MFC worked at first, then did nothing. Slapping the bezel on the Apple icon did, at least half the time. Under repair warranty another 2 months. Now what the hell do I do???

 

[Brachaci]

as a first thing I would recommend you to record it. Just use your phone and record a video while it is happening. With a clear date and time proof, rpm proof, activity monitor proof (with all system processes visible) and then take it back to the service. I’ve done the same. In my case the authorized apple service did a restore of the T2 chip and as of that it did not happend again. I talked to the guy who did the restore and he told me that it is so specific issue, that next time it will happen I should record it again and then they’ll replace the whole motherboard. They probably do not know what is causing it, so there isn’t much to do for them as well….it’s just my opinion not a fact, though.

 

[RoboCop001]

Same fan problem, refurb 2020 27" 3.8 GHz 8-Core Intel Core i7 iMac. 3 visits to Apple store and no answer. one SSD wipe and OS re-install to Monterey 12.4. Fan would speed to 3600 rpm, usually on wake-up, with no apps running. MFC worked at first, then did nothing. Slapping the bezel on the Apple icon did, at least half the time. Under repair warranty another 2 months. Now what the hell do I do???

as a first thing I would recommend you to record it. Just use your phone and record a video while it is happening. With a clear date and time proof, rpm proof, activity monitor proof (with all system processes visible) and then take it back to the service. I’ve done the same. In my case the authorized apple service did a restore of the T2 chip and as of that it did not happend again. I talked to the guy who did the restore and he told me that it is so specific issue, that next time it will happen I should record it again and then they’ll replace the whole motherboard. They probably do not know what is causing it, so there isn’t much to do for them as well….it’s just my opinion not a fact, though.

Definitely insist on replacing the whole logic board. Rickbot, perhaps you can show them this thread as well. The logic board replacement is what ended up "fixing" mine. No problem since! And it's been 1.5 years.

 

[Rickbot]

Thanks, gents. This is way more work than it needs to be just to get Apple to come through on this.