03/21/2017:
I'm back..........
Posting response to my own post from just over a year ago.
For reasons I can't fathom, my Brother HL-L2340DW printer will not print via wireless network again. Seemingly randomly, problem recurred again today. Unable to print via wireless network.
Trying to print via home wireless network from desktop iMac (OS X El Capitan; 10.11.6). Have been able to print without problems for months. Today, no go. When I try to print, for example a MS Word document, printer logo appears in bar at bottom of desktop screen but job does not print. Clicking on logo, print queue shows up with message for job that notes "printing...looking for printer" but above that it says "printer is not connected".
Have tried the iPV6 enable trick but does not work this time. Interestingly, IPV6 *was* disabled when I entered printer IP address into browser and checked settings. But enabling it does not solve problem this time.
Have tried deleting printer and re-install of printer and driver software (big pain and time suck). have tried firmware update as well.
have tried the simple stuff, too (turned router on/off, turned printer on/off, turned computer on/off).
have now tried everything I can think of and printer is useless/will not print via wireless network.
Still able to print from my spouse's windows desktop via the same wireless network.
Given my experience with Brother support, doubt they will be helpful. (Last year, after 45+ minutes, help line person stated if printer could print test page from printer interface and WLAN report showed connection was OK, there was nothing wrong with printer and there was nothing Brother could do to help solve wireless printing issues.)
Life is too short. My next step may be to buy a different brand of printer that will work with an iMac via a wireless network. Having spent hours and hours on this months ago and again today, my time is worth more than the cost of a new (non-Brother) printer that will work. Will let spouse continue to use the Brother.
Too bad we seem to need 2 different printers in one house, though.