iMac 27" (late 2012) is switch off but fan run at full speed

Haukenpo: Is your 3rd iMac working okay now? I'm on my #2 new 27" iMac (ordered originally in late December, and the replacement unit sent to me in early February) ... and the second unit is doing the same thing ... again. When I power down, the fan comes on strong. The folks at the Apple store seemed totally stooped by this. Any update on your end? Thanks for anything you can share.

I set hibernatemode to 3

using a different powered USB hub and I have no problems now.

I am using this shell function to monitor the hibernatemode for any changes, and for the last three or four days there has been no changes, and no problems waking from sleep.

function showhibernate() {

while true

do echo -n `date` " ";pmset -g|grep hibernatemode;sleep 10

done

}

put the above in .bash_profile, source .bash_profile, and type showhibernate

or just type into the terminal the following one line:

while true;do echo -n `date` " ";pmset -g|grep hibernatemode;sleep 10;done

I believe that these are two separate issues.

my first Mac had the "fan runs when powered down", and I believe that this is independent of the USB hub.

the second and third did NOT have this issue (but I only had each for about two weeks)

however, both the second and third would NOT wake up from sleep, which does seem to be affected by a certain brand of USB hub.

now, that I have a different brand (only four vs seven) hub plugged in, my hibernate mode stays at 3 (vs changing to 5 or 7 when plugging in the original USB hub)

so I canceled the fourth replacement, and I am keeping the third one.

-avi

Dear Richard: I have posted with my 'fan issues' on this thread a couple of times. I still have not fixed my issue, and as I was reading back through the strand again today, I read your post of Feb. 28th again. Our situations seem to be pretty much identical. I'm wondering if you were able to resolve the issue yet? And if you did, if you were able to figure out the problem without having to have Apple replace the iMac again? Thanks for letting me know; I appreciate your feedback.

May I know what is your current Mac hibernate mode? you used below command to reset the hibernate mode?

sudo pmset -a hibernatemode <integer>

Haukenpo: I've set it to 0, and to 7. Gone back and forth. Does not change the behavior of the fan powering on full-blast whenever I shut down the computer.

Have called Apple again, and they seem dumbfounded. They've asked me to bring the iMac back to the Apple Store again. I'm sure they will order another new unit again. What's to say the next one won't do the same thing. Other than I don't think I will plug a USB hub into it. ???

Hello to everyone,

I had a similar 'fan runs when I power down the iMac' issue with my 2013 27' iMac purchased in January.

My Imac has worked flawlessly until yesterday, after a few days ago I started to use the usb hub (powered USB 3.0 4 ports hub).

Yesterday morning after working normally I put the iMac in standby mode (menu apple-stop); yesterday evening I try to wake up the iMac with no responses. I tryied to shut down by holding down the power button without any results. At the end I unplugged power cord, at which point the fan starts to rotate at high speed, stopping only when I turn on the imac.

After that the imac works on a regular basis when turned on. Then when I turn it off (apple menu-shutdown) the fans start again until I pulled the plug.

I tried resetting smc and pram, without success.

Has anyone else found any new info about how to fix this issue?

Thanks in advance for any help,

Daniele

Hi Haukenpo,

this evening I'll check the brand and model and I'll tell you.

Calling the apple service I realized that the only thing they will do is to repair / replace my Imac, but seeing that this appears to be a defect linked to the usb hub, I would like to figure out if it is fixable without replacement (because not even the replacement solves the problem).

Daniele

I have the same issue. I purchased this hub on NewEgg back in March or so:

http://www.newegg.com/Product/Product.aspx?Item=0J2-0020-00001

I have created a case with Apple and asked a senior advisor to escalate the issue to Engineering. I haven't heard anything back. The senior advisor recommended taking the unit into a Apple Authorized Service Provider (AASP) or Apple Store for troubleshooting and diagnostics. Fixing this issue requires replacing the logic board. I rarely turn off the machine so it does not bother me enough to take it in for service.

My hope is that a future firmware update will resolve this issue so I am holding out for that. :-/

Hello Haukempo,

my hybernate mode is set to 3...

My usb hub is a Goobay mod. 95347 (www.goobay.de).

The fan still running...

Daniele

Morning guys! I'm experiencing the same problem...did you solve it? Anyway, I don't have any USB hub plugged in my iMac! Only USBs plugged in are my printer and my iPhone cable!!! It started doing this strange fan thing for no reason!!!

Got Motherboard replaced and problem went away.

I have no new information other than what I had already shared on this thread. Sorry to hear you are dealing with this too.

Yes, two days ago i went to a Genius Bar with this problem (iMac 21,5) and they can´t find the solution.

All the checks was ok, and the PRAM and SMC resetted.

⚠ This iMac always had problems with USB devices as mouses and headsets.

-3 headsets and 1 usb mouse broke down .

-You can also hear audio few clicks if the microphone is used from the input minijack .

Coincidence?

Worst of all, it went without my computer and they did not give me a solution.

The warranty expired seven days ago.

😟