El Capitan Not Allowing Mac To Sleep

Just a note to say that 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!

10.11.2 installed and no difference. Sleeps OK but when wakes up the computer has lost track of my printers. Have to restart. Disappointing, Apple. Some word from you that you're listening would be nice

AHA!!!! I discovered that the iMac only loses connection to anything connected to my USB hub! This may be a third-party issue and not Apple's. My humble apologies for assuming that Apple were to blame, if that's the case. I will re-post if the problem persists with a different hub

I've had this problem a couple of times and found an easy fix, at least for one situation... Google Chrome allows preventing sleep, so something open in one of my tabs was the culprit. To fix this case:

- open Activity Monitor to confirm that Chrome is preventing sleep (Applications --> Utilities --> Activity Monitor, then click the "Energy" tab and look under "Preventing Sleep")

- in Chrome's options list (top-right corner) choose "More Tools" then "Task Manager". Click "CPU" heading to sort, and see if any tab is using more CPU than the "Browser" itself. If so, visit that tab and close it. Then re-check in Activity Monitor that the "Yes" is now a "No" (note it takes a few secs to update).

That fixed it for me a couple of times. In neither case was there anything obvious in the offending tab re: why it needed to prevent sleep, just badly-written S/W I suppose!

I have a Macbook Pro, with OSX 10.11.2, and an external USB hard drive that I never removes. Before I upgraded to El Capitan, the external disk LED have gone black after apron 60sec. after the computer is closed. This has worked for several years... However now, with El Capitain it NEWER goes black. Even if I tell the system to sleep the hard drives after 5min...

The problem is that the MacBook now uses power when the MacBook is closed, so after a day or two it is out of power. The totally changes the way we can use the Mac, if this continues, one of the major reason for using Mac is gone.

Sorry,I hade the Power settings wrong. OK Now.

Thanks for pointing out the Energy tab on the Activity Monitor.

I found two apps (TeamViewer, Sibelius 7.5) listed as "Preventing Sleep." Neither quitting those nor rebooting addressed my symptoms, which were no sleep or screensaver with El Capitan since the 10.11.3 update. (iMac 3.1 GHz Intel Core i5)

However, restarting in single-user mode and doing a fsck solved my problems, and now I can't replicate the error even when running those apps.

http://osxdaily.com/2013/08/07/how-to-repair-a-mac-disk-with-fsck-from-single-us er-mode/ gives a simple explanation of how to do this.

Hope this helps.