iMac is Rebooting

My iMac has been rebooting by itself. I haven’t seen it happen. I can see the reboot times in Terminal. I’ve been looking at the system log in Console but I need some help trying to diagnose the cause of the problem.

Ok. Can you help me figure out how to get the solution from either of them? It sometimes reboots when I’m watching Apple TV and it’s driving me crazy.

When did it start? After any hardware (internal or connected) or software or network changes? If not, it may be a chip that’s failing.

Reset the SMC

  1. Shut down the mac
  2. Unplug every wire
  3. Push and hold the power button for 5 seconds
  4. Reconnect Powercord, keyboard and mouse
  5. Power back on
  6. Reconnect other USB / Network cables

Hope this helps,


Have you checked the system logs yet? Something might be crashing. Use the console app.

It could be something very low-tech. A friend was struggling with this issue, and I found that the power cord was making intermittent contact where it was inserted into the rear of the iMac; it wasn’t fully inserted, although only by a millimeter at most. It wasn’t seated well, and I think it may have been a cord from an earlier model of iMac because the flange part of the plug couldn’t be made flush with the back of the iMac. For whatever reason, I pushed hard on it and it solved the problem, although if it had been my iMac I would have found a cord that fit better.

Thanks. My iMac is plugged into a surge protector, tight as a drum. If the problem was the surge protector at the wall, other devices would have shut down, and that isn’t any case, the wall connections are tight.

I have checked the logs but I’m not always sure what I’m looking at. I haven’t seen any common denominator. And the log only shows the current day.

I’m not sure when it started. It always happens when I’m away from the computer. I’ll look at the screen and see that Firefox is in a different space because it hasn’t been assigned one, and the open tabs are closed. Other times, I’ll be in the living room watching something on Apple TV and I lose the connection to my iTunes Library.

Terminal tells me the uptime and the reboot times. So I know for sure the machine is rebooting.

This morning, I began to wonder if the problem started when I added OWC RAM about a week ago. About This Mac reports the correct amount of RAM. Maybe the RAM is defective or not seated properly?

Unfortunatley OWC memory isn’t what it used to be.
In the past year I had a couple of instances where OWC memory was defective and needed to be returned under warranty.

I just ran a check (starting up pressing D) and came back with No Issues Found. If it continues, I’ll re-seat the RAM.

Trying this now. Thanks.

If you read my posting more closely, you will see that the issue was at the OTHER end of the power cord. Where it plugs into the back of the iMac. It’s worth checking! The mac would run fine, but some movements (not all) of the table it was on or of the Mac itself would make it shut off. Pushing it in less than a millimeter made all the difference – but if it were my mac, it would feel an awful lot like the Sword of Damocles and I would replace the cord. The owner is still using the same problematic cord, to the best of my knowledge.

Update: The problem was my OWC RAM. As I mentioned earlier, I recently added more OWC RAM to my iMac. At the time the problem occurred, I was using four 8GB OWC chips, two were older and two were about a month old.

I searched and found a forum where people where having the exact same problem. (Note that the original post is from 2016, so this problem has existed for at least three years.) Their Macs were rebooting while it was idling and while they were using iTunes. All of the people reporting the problem were using OWC RAM. One person reported that when they contacted OWC (aka Mac Sales), they were told the problem could be due to residue left over from the manufacturing process and to try using a pencil eraser to clean the contacts. No one reported that the “fix” worked.

So, I called Mac Sales and they gave me the same residue/pencil eraser story. I told them that since no one reported that worked, I wasn’t going to waste my time, and they sent me an RMA ti return the RAM (no prepaid label, though). I figured the “fix” was worth a try, so I pulled out the RAM, rubbed the chips with an eraser, and used some dust-off to blow out the bay. I firmly reseated the RAM. My iMac continued to reboot.

I ordered four Crucial 8GB chips from Amazon and it arrived the next day. I removed the four OWC chips, installed the Crucial RAM, and left the iMac on over the weekend. No reboots.

I understand that bad RAM can come from any supplier. But considering my experience and looking at others who had the same problem, I would not recommend buying OWC RAM. I should add that although OWC is going to refund me for the two new 8GB RAM chips, I also removed the two older chips, which are out of warranty, so I’m out about $100.

1 Like