iMac fan runs full speed on shut down

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iMac fan runs full speed on shut down

Hi Everyone, this has probably been discussed before, but I may have some new information to add that could interest the tech savvy people out there.

My iMac runs perfectly fine; more or less as it did when it was new. In OS X, when I shut down the computer, the fan runs at full speed indefinitely, unless I unplug it or boot back up. When running, the fan is perfectly normal (increases speed a bit when doing something taxing). I've never heard it at full speed before until this started happening. After following the SMC reset procedure with no luck (I'd like to add that the SMC reset only says it relates to fan problems when the computer is ON), I searched a bit and noticed there are one or two cases where a problem like mine was believed to be a motherboard issue, and therefore a costly fix.

However, here's the fun part. When booted into Windows 8.1, shutting down the iMac does not cause this issue to occur. It stays silent, as it should, even if I disconnect then reconnect the power. This leads me to believe it's unlikely to be a motherboard issue. However I've wiped, restored, and reinstalled fresh copies of Mountain Lion, Mavericks, and Windows 8.1, and the result is still the same: if I don't want to have to unplug it from the wall, then I have to use Windows to shut it down.

So then, my questions are these:

-What is the difference between shutting down from OS X and shutting down from Windows?

-Is an operating system allowed/able to touch BIOS settings?

-Is it possible to still be a hardware problem, given this difference?

My default OS is OS X, and it makes no difference if I change that to Windows. I also did a PRAM reset, even though that has nothing to do with fans...

I'd certainly like to avoid a costly repair, if it's just something that a future software update will fix.

Thanks in advance!

-Jon

--------------------------------------------------------------

iMac 27", Late 2012, 3.4GHz i7, 3TB Fusion Drive, 16 GB, OS X 10.9.4

iMac, OS X Mavericks (10.9.4)

Posted on Aug 27, 2014 2:58 PM

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Answer 1

rkaufmann87

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140,418 points

Aug 27, 2014 3:28 PM in response to DvorakUser

Reset the SMC 2-3 times back to back following the directions in iMac SMC and PRAM reset

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Answer 2

DvorakUser Author

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Aug 27, 2014 7:19 PM in response to rkaufmann87

This is a joke, right? ...as we sit back and recall the popular definition of "insanity"... 😕

I don't mean to be rude, of course, and just in case you weren't actually joking, I tried it. Thanks anyway.

-Jon

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Answer 3

rkaufmann87

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140,418 points

Aug 28, 2014 5:59 AM in response to DvorakUser

Well I can tell you don't appreciate someone attempting to assist you, I'm done with you .

Good luck sport.

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Answer 4

DvorakUser Author

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Aug 28, 2014 9:40 PM in response to rkaufmann87

No no, I appreciate all new ideas. It's just frustrating doing the same old procedures over and over and getting nowhere... I'm sure you can understand.

Do you have any other ideas?

Thanks.

Edit: To explain my snarky comment better, I have just never heard of 2-3 resets bring success where 1 has failed. And certainly I had done the reset on a couple occasions before, just not multiple in a row. Has that actually been the case in the past? It seems kind of ineffective as a solution if 2 times does something different than just 1... but again, sorry to have offended.

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Answer 5

rkaufmann87

Level 10

140,418 points

Aug 29, 2014 5:55 AM in response to DvorakUser

DvorakUser wrote:

No no, I appreciate all new ideas. It's just frustrating doing the same old procedures over and over and getting nowhere... I'm sure you can understand.

Do you have any other ideas?

Thanks.

Edit: To explain my snarky comment better, I have just never heard of 2-3 resets bring success where 1 has failed. And certainly I had done the reset on a couple occasions before, just not multiple in a row. Has that actually been the case in the past? It seems kind of ineffective as a solution if 2 times does something different than just 1... but again, sorry to have offended.

The SMC reset does not always work the first time, sometimes it takes several attempts for it to take. If you have any external peripherals attached (printers, scanners, EHD, etc....) disconnect them while doing the SMC reset, one or may can be the cause of the problem.

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Answer 6

DvorakUser Author

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Aug 29, 2014 12:32 PM in response to rkaufmann87

I see, I suppose that's understandable. I don't have wired peripherals hooked up to it these days.

So where are you getting this information from? And if you're correct, then why doesn't Apple's SMC reset procedure describe this? It also doesn't describe anything to do with fan speed when the iMac is off as being one of the symptoms that a reset could fix, but I guess the whole "try it anyway cuz why not" thing has worked in the past for other things...

So being that the SMC isn't my problem, I was hoping someone with Windows or BIOS knowledge would pipe in to propose some ideas regarding the behaviour described in my original post. I'd just like someone to assure me it's not a motherboard problem, or explain how it could still be the motherboard, given the different behaviour observed when shutting down with different OS's.

Thanks.

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Answer 7

den.thed

Level 9

77,044 points

Aug 29, 2014 4:47 PM in response to DvorakUser

Sounds like maybe it is either not shuting down or starting up when it is plugged back in.

Try this, go to: Apple > System Preferences > Energy Saver and uncheck "Startup automatically after a power failure" then shut down, unplug and replug or do the SMC reset.

Now then if the fan come on when you plug it back in, run the Extended Apple Hardware Test or contact your local Apple Service Provider and have them check it out.

Using Apple Hardware Test

http://www.apple.com/support/contact/

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Answer 8

DvorakUser Author

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Sep 2, 2014 9:03 AM in response to den.thed

Hey, thanks for the response.

The "Startup after power failure" option was not checked.

I'll try the Extended Hardware test when I get some spare time again - probably tomorrow night. After that I suppose it is time to either take it in for service/diagnosis, or just keep using Windows to shut it down. Sleep mode is unfortunately not an option because it eventually goes into hibernate state, which has the same problem as turning off. I don't like to leave the computer on all night, just from a power-conscious point of view (but yes, I know today's iMacs use very little power). I have it on a power bar now, so I just flick the switch off when I power down. It's not bad as a temporary solution - perhaps permanent if the shop says they have to replace the motherboard.

As for contacting Apple... I had a 1-hour conversation with them about my iCloud account, because it suddenly stopped working on this Forum site (hence the new account with no points). Anytime I sign in, it forwards me to the "page not found" error page. This happens even if I sign in on the apple store then click over to here. If my login info has an open session, then Discussions just doesn't work. They were completely baffled (understandably), because the account works on iTunes, iCloud.com, Apple store, and everywhere except Discussions. I was on the phone with them for over an hour - and the kicker is, even after telling them the same thing happens in other browsers, from other computers, they actually forwarded me to the iMac team. This is when I lost faith in Apple support. When one of the staff asked why I don't just phone about the issue, instead of trying to get access to the forums just to post about it, I told them I didn't want to pay $50/hr (or whatever the insane rate is for Mac hardware issues), only to be put on hold and sent around between departments, just to be told I need to send it in for service, which I'm probably not going to do if it's the motherboard. They never did get back to me about my account issue...

Anyway, sorry for the rant, I'll keep you posted about the hardware test and more SMC resets. 😕

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Answer 9

DvorakUser Author

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Sep 8, 2014 9:05 PM in response to DvorakUser

Hey guys, sorry for the late response.

The Extended Hardware test didn't find anything abnormal with my iMac.

I'm assuming I've exhausted everyone's ideas by this point. I'll try to find some time to take it to the shop. My city only has 1 that services Macs though, and the hours suck, so I'm not when that'll happen. Anyway, thanks for trying to help. 🙂

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Answer 10

Mar 8, 2015 3:50 PM in response to DvorakUser

Hey, sorry to resurrect this thread but has anyone else experienced this issue? I just brought mine into the shop and it looks like it's going to be a $700 logic board replacement. I hadn't tried dual-booting with Windows though. That seems weird that one OS would do the trick and not the other.

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