My iMac does not sleep after install of El Capitan

As with others, doing all the various resets (PRAM, etc.) did nothing for me, either.

Given the breadth of complaints and hardware involved, it does point to an El Capitan problem. More annoying, Apple now seems quite content with regularly releasing new operating systems, knowing full well there are some pretty significant bugs. (Don't even get me started with what iOS 9.1 did to my iPhone 6+'s general performance.)

After resetting the printing system my iMac (2011) sleeps again:

https://support.apple.com/kb/PH18614?viewlocale=en_US&locale=nl_NL

This helped in my case, thanks for the tip!

I've set computer sleep to 1 min. afterwards to test it. - It didn't work the first time, but on the 2nd or 3rd try my iMac did - finally, after a long time - sleep automatically. From then on it seems to be activating sleep mode correctly automatically, so far.

( while looking at output from pmset I've also quit Sounflower/bed GUI - audio driver is still installed. If you don't know what sounflower/bed is you don't need to be concerned about it.

But have no idea if it is connected though.)

Did you get a solution to this? In my case the pmset -g assertions query shows:

Idle sleep preventers: IODisplayWrangler

System sleep preventers: .Display_boot

I tried all the suggestions in this thread, including resetting printer. Funny, just before this started my printer played dead for a while, so thought that would help, but didn't.

Anyone know anything else I can try?

About two weeks ago I did a re-install of El Capitan.

You can do that easily by holding Command+R when restarting your Mac.

You need an internet connections because you have to download a fresh OS.

This helped me for now.

Just once it seems to be bothering again,

but a simple restart made my Mac sleep again.

I'm cautious to declare this problem as solved for ever.

I want to hold this issue in observation.

But I'll keep in touch.

If within a month it is still nicely sleeping ...

Thanks, I was thinking I might have to reinstall El Capitan.

UPDATE: The latest OS X update, 10.11.2, solved the Sleep issue for my iMac. I didn't try the re-install idea, so I hope Apple did address the issue in the latest update and fixed it. If so, thanks Apple gang!

Such an update can be a similar cure as a reinstall.

Cause an update is a reinstall as well.

> After resetting the printing system my iMac (2011) sleeps again:

> https://support.apple.com/kb/PH18614?viewlocale=en_US&locale=nl_NL

This helped me.

In my case, the "pmset -g assertions" check showed that Spotify's promotional video was playing and keeping the display from sleeping. So I quit out of Spotify. Late 2009 iMac.

Look at which task is keeping PreventUserIdleDisplaySleep 1.

In my case, it was Spotify playing a promotional video. Closed Spotify...and fixed!

I just received my late 2015 27" iMac with El Capitan and I'm seeing the same problems with it not staying asleep. I manually put it to sleep via the Apple menu but it wakes itself up after some time. I'm on OS X 10.11.3.

Mine went back to going to sleep as normal after reseting the printer system. I had an old printer still on the list and few others. Will just put back on my current printer. Thanks!

For your information, SMC Reset worked on my side.

> After resetting the printing system my iMac (2011) sleeps again:

> https://support.apple.com/kb/PH18614?viewlocale=en_US&locale=nl_NL

Finally! This worked for me. Thanks.