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2011 iMac reboots when waking from display sleep

mrbobdobolina

mrbobdobolina

macrumors member
Original poster
Feb 28, 2016
83
64
Hi all. Wondering if anyone has advice or suggestions.

I have a 2011 iMac that I use as a home server of sorts. I have it set to never go to sleep, but I have the display set to sleep after 15 minutes.

I've run it like this for months without issue but lately when I move the mouse to wake the computer the machine reboots. It goes from a dark screen and the next thing I see is the grey startup screen. Reminds me of a kernel panic.

Once or twice it's gotten caught in a boot loop. The desktop loads up and boom, reboot. A few times it never even got that far. Others it got a little farther.

I found that if I unplugged my USB hub and thunderbolt drives the boot-loop would stop and it would run normally. While not super convenient, I decided to run without those for a while. But it happened again.

So I re-installed High Sierra. (10.13.6) I just did a re-install over the system. I ran the updates as needed. I did a clean install onto an SSD a little over a year ago, and I don't use the computer much, so I've kept it mostly clean of extra apps, though it has a few syncing programs and other utilities. (Sync.com and Google Drive)

It seemed to be working again, but tonight it just rebooted on me when I grabbed the mouse.

I'm suspicious that the machine is actually going to sleep, despite my settings, because it takes so long to wake up sometimes. When the machine reboots I usually don't see a "this machine shut-down unexpectedly" window. I don't know if that got deprecated or not, but I'm not seeing it.

Tonight I installed Amphetamine and told it to keep the machine alive indefinitely, but allow the display to sleep. I'll see if this makes any difference.

Has anyone had similar experiences or ideas for things to test? Thanks a bunch.
 
Try resetting the SMC to see if that helps. Also... your internal drive, is it an SSD or a regular spinning hard drive? Either one, try running First Aid from Recovery to see what it says. Sudden reboots are usually related to hardware problems so that's where you should probably focus on when trouble shooting.
 
chscag said:
Try resetting the SMC to see if that helps. Also... your internal drive, is it an SSD or a regular spinning hard drive? Either one, try running First Aid from Recovery to see what it says. Sudden reboots are usually related to hardware problems so that's where you should probably focus on when trouble shooting.
Click to expand...

Ooh, thanks. I'll try resetting the SMC.

It has an internal SSD. (Several years ago I installed an SSD along with the HDD, and for a few years I ran with a home-made fusion drive. Last year when I reinstalled everything I decided to un-fuse the drives.)

First Aid says everything looks fine.

Could it be something with my graphics card?
 
I don't think it's the graphics card. But I'm wondering if your iMac is getting too warm and that causes a reboot? You might want to download Macs Fan Control (free app) and use it to monitor the temperature of your SSD and CPU. It will also tell you the speed of your fans. Your iMac has three fans: CPU, HDD, and Optical Drive. That should help you to trouble shoot the problem.
 
On a whim I ran AHT today. (Took an hour and finally had to install AHT on flash drive for it to work.)

After an hour and a half of testing it returned this error:

4MOT/4/40000003: HDD-1270

That's a fan error? Guessing something with the HDD fan? Would that cause the reboots or overheating?
 
mrbobdobolina said:
On a whim I ran AHT today. (Took an hour and finally had to install AHT on flash drive for it to work.)

After an hour and a half of testing it returned this error:

4MOT/4/40000003: HDD-1270

That's a fan error? Guessing something with the HDD fan? Would that cause the reboots or overheating?
Click to expand...

That's likely the hard drive fan which is not running right. Did you download the program I linked for you? If not, download it and that will show you if there is a problem with the hard drive fan. Like I told you above, your iMac has three fans. You could also have a bad temperature sensor (located on the hard drive itself. Your SSD does not require a temperature sensor).
 
chscag said:
That's likely the hard drive fan which is not running right. Did you download the program I linked for you? If not, download it and that will show you if there is a problem with the hard drive fan. Like I told you above, your iMac has three fans. You could also have a bad temperature sensor (located on the hard drive itself. Your SSD does not require a temperature sensor).
Click to expand...

I did download Macs Fan Control. All three fans seem to be running and I can control them all. Currently it says my HD temp is 106... And the iMac just rebooted on me... Mac came back, I opened the fan controls, played with the fans, set the back to auto and a minute later the machine shut off and turned back on.
 
The "4MOT/4/40000003: HDD-1270" does indicate a problem either with the thermal sensor or the hard drive. The 27" iMacs of that year needed the hard drive thermal sensor to be working or the fan would run full speed. The 21.5" iMac did not have that problem. The machine shutting down like it's doing is probably overheating and the system protection shuts it down automatically.
 
Ulgh. I turned it off last night and this afternoon I booted it back up. I got to the desktop and insta-black screen/reboot. Got to the desktop and let me open Disk Utility, boom, rebooted. Opened disk utility, tried to run first-aid on the HDD, not the SSD, and it said it couldn't. I tried a few more times, and then the machine rebooted.

Upon reboot I opened Disk Utility and tried to unmount the drive, Google Backup and Sync was using the drive. I closed it and ran First Aid on the HDD. Came back clean. Ran it again. Came back clean. The machine rebooted.

I have iStat Menus installed on my iMac... And during all this fuss I noticed that the "HDD proximity" sensor wasn't giving me a reading. The SSD was hovering around 79 and the HDD around 71 degrees according to iStat.
 
Addendum:

At the advice of a friend I installed High Sierra onto an external drive and booted my old iMac using the external drive. It's been running for an hour now without any issues.
 
Try booting the iMac using Safe Mode to see what happens. Who knows, you may have some rogue app that's causing all the problems and sudden boots. You could also have a bad memory module. Might be a good idea to check the memory.
 
chscag said:
Try booting the iMac using Safe Mode to see what happens. Who knows, you may have some rogue app that's causing all the problems and sudden boots. You could also have a bad memory module. Might be a good idea to check the memory.
Click to expand...

Safe mode has me up and running without any issues. Guess I just need to figure out which app/service is giving me grief. Thanks for helping me sort this out.
 
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