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I manually click Sleep but the iMac immediately reboots instead of going to sleep

I'm having two related issues, as follow.. .. these happen about 40% of the time

  1. I manually click Sleep (Apple menu, Sleep) and it appears to be going to sleep but as soon as it would appear to have gone to sleep, meaning the screen goes dark, the hard drive stops, all of a sudden you hear the start up chime and its in the rebooting process and brings me to the log in screen
  2. I set Energy Saver to put the iMac to sleep in 10 minutes and when that time is up, it does the same thing as in #1 above.


This happened out of the blue a few weeks ago, I'm still trying to find the root cause but this is what I have done so far.. ..

  1. Climbed through logs to no avail
  2. Performed an SMC and NVRAM reset. That did not solve it.
  3. Performed a Disk Utility First Aid on the hard drive, it found issues that it could not repair and stated a File System exit code of 8. File system verify or repair failed
  4. Then I noticed my Western Digital firewire backup drive that is attached to my iMac was also flaky, all of a sudden it became read only and Time Machine could not back up to it. It would randomly disappear from Finder and then it would reappear. When it was in Finder, I had no issue navigating it and seeing all the backups
  5. I then rebooted in Internet Recovery Mode and did a hardware test which stated a 4HDD/11/40000004: SATA(0,0) error. That was the only error and I did the loooong extended test.
  6. Upon restarting the iMac using its internal hard drive, it never finished the boot cycle and instead would display a list of DOS like stuff on the screen, very quickly, and then try to reboot again and it did this over and over and over so I thought the hard drive finally bit the dust, maybe the loooong extended test killed it :-0
  7. I then installed El Capitan on a thumb drive using my laptop and booted the iMac from that using the Option key to select a different start up drive and it worked well so I thought the iMac was ok but maybe the hard drive was suspect once again
  8. Since I could read the backup drive, I took a chance and erased the iMac's hard drive and reinstalled the OS (El Capitan 10.11.6). That went well
  9. I then told the iMac to use the backup drive to finish the recovery and that went well and I was back up and running.
  10. I then erased the backup drive and did a full "first time" backup which also went well and it was read/write again instead of read only.


At this point I was back up and running and putting the iMac to sleep successfully until about the 4th or 5th time when it rebooted instead of going to sleep so the issue remains. At this point I .. .


  1. Ran Disk Utility on both the internal hard drive and the backup drive and both passed
  2. I have not yet run another hardware test from Apples internet recovery server but do plan to while this request for help percolates. When running that hardware test before, the only thing it found was that hard drive error I listed above. I ran both the short and long tests.


In Summary: 2011 27" iMac running El Capitan. All works well except for it rebooting instead of sleeping about 40% of the time. To be clear, it reboots instead of sleeps at the moment it tried going to sleep, not at some point after it sleeps. Once asleep, it does not wake up unless I wake it via the space bar and when it does wake up, it wakes up fine.


I uploaded a few of the screenshots as taken from my phone. Any ideas as to the root cause and corrective action would be very appreciated.



iMac 27″, OS X 10.11

Posted on Sep 22, 2021 2:08 PM

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Posted on Oct 9, 2021 3:45 PM

The root cause is the hard drive failure. Without a working hard drive, you aren't going to go very far with the computer. You could have an authorized service center disconnect the internal hard drive, and help you setup an external hard drive on the computer as your primary. They might even be willing to help you swap in an internal SSD for optimal speed. But don't try this repair yourself. Even as a certified tech I can tell you that putting it back together can often lead to startups with high fan speed, meaning a step was missed, or damage to internal components.



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5 replies
Question marked as Top-ranking reply

Oct 9, 2021 3:45 PM in response to Bgnmarty

The root cause is the hard drive failure. Without a working hard drive, you aren't going to go very far with the computer. You could have an authorized service center disconnect the internal hard drive, and help you setup an external hard drive on the computer as your primary. They might even be willing to help you swap in an internal SSD for optimal speed. But don't try this repair yourself. Even as a certified tech I can tell you that putting it back together can often lead to startups with high fan speed, meaning a step was missed, or damage to internal components.



Oct 17, 2021 10:55 AM in response to Bgnmarty

Ok, I've now replaced my 10yr old + spinning HD with an SSD drive. This iMac is now blazingly fast!!! However, it still exhibits the same issue of rebooting instead of going to sleep when I put it to sleep either manually or via the Energy Saver in System Preferences :-( I ran the extended hardware test and everything passed.



When I built the SSD, I used Apples Internet Recovery to download and install the OS (High Sierra) and then I used Restore from the recovery menu to Restore from my Time Machine backup. I am now wondering if there is some sort of corruption in the Time Machine backup somewhere, maybe in a file, an app, etc, otherwise it would appear I have an electronic issue but would have thought the Hardware test would have picked it up, then again, this issue only happens about half the time.


Possibly I have a corrupted Preference file somewhere...but wouldn't that make it happen every time I try to put it to sleep??? Anyone have any ideas???

Oct 10, 2021 5:47 AM in response to a brody

Not to worry a brody, I've had my iMac apart a few times, its not that bad taking it apart and getting it back together. In fact, there was a warranty claim on it when my GPU fried, Apple had me take it to an authorized repair center, they replaced the GPU but did not seat one of the connectors properly. I took it apart, found the connector, reseated it and reassembled the iMac, no issue.


I have already ordered a 1T SSD drive kit, should be here by next weekend. I'll first plug it in the USB port and clone it, then will replace the internal hard drive. Since all else is working properly, I hope the hardware error I see when running diagnostics is correct and this will solve the sleep/reboot issue as its driving me nuts. I also hope to enjoy a faster puter as a side benefit :-)


Thanks for chiming in, its always good to get others take on the issue as a confirmation to what I am seeing and thinking. My, you have a lot of points!


Oct 17, 2021 5:44 PM in response to Bgnmarty

One of those odd things. There is a heat sensor which needs to be connected for proper functioning. Check with a certified tech that the job was done right.


Rember is another RAM testing utility which sometimes is better than Apple's own. The RAM could be bad. The CMOS/PRAM battery could be bad. On some machines it is a capacitor and unfortunately means a logicboard swap.

Oct 18, 2021 6:09 AM in response to a brody

Heat sensor for what? The hard drive? If that is what you are referring to, the sensor came in the kit I bought and it is attached to the new SSD. I just removed all the RAM and reinstalled the original RAM that came with the iMac, however its still rebooting instead of sleeping. Yes, the little battery could be shot by now, its over 10yrs old, I can replace that easily enough. If that doesn't fix it, then I guess its pointing to the logic board - ugh. I just tried shutting it down so I could replace the RAM and once it appeared to be shut down, it automatically restarted with a fresh boot :-( So now its not sleeping or shutting down some of the time, not every time, just around 50% of the time. So it doesn't appear to be a hard failure, otherwise it would act improperly 100% of the time. At least now with the new SSD installed, it reboots within just a few seconds :-)

I manually click Sleep but the iMac immediately reboots instead of going to sleep

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