Suddenly cannot join 5 Ghz network (802.11n)

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Level 1

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Suddenly cannot join 5 Ghz network (802.11n)

I have a 15 inch macbook pro retina mid 2012 running on OS X Yosemite 10.10.4.

I have a wireless network at home based on the latest Airport Extreme unit (with support for 802.11ac). The network uses WPA2 Personal security, with the 5GHz network enabled. I have made no changes to my wireless base station in the last 2 months (no changes in settings, no changes in firmware etc.).

The 5Ghz network at home is the top selection in the network settings and normally my macbook pro automatically joins this network. Three weeks ago while I was still running on 10.10.3 I noticed that when I opened the lid of my macbook pro, it took a while for my mac to join the 5 GHz network (the grey Wifi icon would show the animation of the lines becoming dark in a wave like fashion and after about 10 secs my mac would join the network). In the past my mac would immediately appear to have joined the network so I noticed the change in the behaviour. Once the computer joined the network however there were no problems.

About two weeks ago, my mac stopped joining the 5 Ghz network. This was still on 10.10.3. I received a message saying the a time out had occurred and the wifi icon remained light grey (with no exclamation mark in it). If I tried to select the network I subsequently got a message saying that I needed to move closer to the airport base station or run diagnostics. The computer had no problem joining the 2.4 GHz network.

No other devices at home have had trouble joining the 5 Ghz network. 3 ipads, a macbook air, another macbook pro and 4 iphones continue working fine with the 5 Ghz band. I also did a factory restore of the Airport Extreme and set up a different network with a different name and my mac could not join the 5 GHz band.

All this led me to conclude that the problem lay with my mac. It is either a hardware problem or a software problem.

The internet recovery, has shown no hardware problems with the mac.

In terms of software, I have tried cleaning the DNS cache, resetting the NVRAM, SMC, fixing permissions but nothing helped. I also cleaned up the network from the keychain items but this also did not help. I also started the mac on the recovery partition and the problem remained. Also starting in safe mode did not resolve the problem. All this indicated that the problem was hardware related.

In the mean time 10.10.4 was released but the problem remained.

To my amazement the problem disappeared when I booted the mac from a super duper external clone. Once I did this I could join the 5 Ghz network. After rebooting from the internal SSD, the problem disappeared! The problem reappeared about a week later and I ran the internet recovery to check for hardware defects again. At start up you are asked to join a network and I selected the 5 Ghz network. I could join the network with no problems and after rebooting my normal OS X partition can again join the 5 Ghz network. This is totally bizarre behaviour. Does anyone have any clue what is going on?

MacBook Pro with Retina display, OS X Yosemite (10.10)

Posted on Jul 5, 2015 9:31 AM

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Answer 1

Linc Davis

Level 10

209,535 points

Jul 5, 2015 9:44 AM in response to dlinar01

Take each of the following steps that you haven't already tried, until the problem is resolved. Some of these steps are only possible if you have control over the wireless router.

Step 1

Turn Wi-Fi off and back on.

Step 2

Restart the router and the computer. Many problems are solved that way.

Step 3

Change the name of the wireless network, if applicable, to eliminate any characters other than letters and digits. You do that on your router via its web page, if it's not an Apple device, or via AirPort Utility, if it is an Apple device.

Step 4

Run the Network Diagnostics assistant.

Step 5

In OS X 10.8.4 or later, run Wireless Diagnostics and fix the issues listed in the Summary, if any.

Step 6

Back up all data before proceeding.

Launch the Keychain Access application in any of the following ways:

☞ Enter the first few letters of its name into a Spotlight search. Select it in the results (it should be at the top.)

☞ In the Finder, select Go ▹ Utilities from the menu bar, or press the key combination shift-command-U. The application is in the folder that opens.

☞ Open LaunchPad and start typing the name.

Enter the name of your wireless network in the search box. You should have one or more "AirPort network password" items with that name. Make a note of the name and password, then delete all the items. Quit Keychain Access. Turn Wi-Fi off and then back on. Reconnect to the network.

Step 7

You may need to change other settings on the router. See the guidelines linked below:

Recommended settings for Wi-Fi routers and access points

Potential sources of interference

Step 8

Make a note of all your settings for Wi-Fi in the Network preference pane, then delete the connection from the connection list and recreate it with the same settings. You do this by clicking the plus-sign icon below the connection list, and selecting Wi-Fi as the interface in the sheet that opens. Select Join other network from the Network Name menu, then select your network. Enter the password when prompted and save it in the keychain.

Step 9

Reset the System Management Controller (SMC).

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Answer 2

dlinar01 Author

Level 1

0 points

Jul 5, 2015 10:02 AM in response to Linc Davis

Dear Linc Davis,

Thanks for the quick reply. I have tried all the steps you suggest but none worked. Strangely, joining the network from internet recovery (or from an external disk clone) does seem to resolve the problem.

Best regards

dlinar01

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Answer 3

Linc Davis

Level 10

209,535 points

Jul 5, 2015 12:13 PM in response to dlinar01

If you don't already have a current backup, back up all data, then reinstall the OS.* You don't need to erase the startup volume, and you won't need the backup unless something goes wrong. If the system was upgraded from an older version of OS X, you may need the Apple ID and password you used.

There are ways to back up a computer that isn't fully functional. Ask if you need guidance.

If you installed the Java runtime distributed by Apple and still need it, you'll have to reinstall it. The same goes for Xcode. All other data will be preserved.

*The linked support article refers to OS X 10.10 ("Yosemite"), but the procedure is the same for OS X 10.7 ("Lion") and later.

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Answer 4

dlinar01 Author

Level 1

0 points

Jul 5, 2015 12:52 PM in response to Linc Davis

Thanks again. I am aware of this option and I should be able to do this without taking any risks; I have recent clones of my hard disk, time machine back ups and all my files are in dropbox. Nevertheless I would like to try and understand what causes the problem. Simply reinstalling the OS reminds me of the way Windows people deal with problems...

If I find no answer I will end up doing what you suggest.

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