WiFi Problem Solved via SMC Reset

Every so often I run into a problem that just doesn’t make sense. I ran into one like that today. A MacBook Pro could not connect to the wireless network, even though it worked fine yesterday and as far as anyone could tell, nothing had changed. The network was visible under the Airport menu, and other devices (an iPad, an iPhone, and my own MacBook Pro) were able to connect. But the other MacBook Pro– the one that connected to the WiFi yesterday– asked for a password every time we tried to join the network, and even though we knew the network’s password it never was accepted. The error message said “Connection timed out.”

Rather mysterious. It worked yesterday, but not today. And other devices connected to the network just fine.

Here’s what I tried.

  1. Restarted the MacBook Pro (no good)
  2. Turned the WiFi off on the MacBook Pro and then back on again (no good)
  3. Restarted the Airport base station– actually a Time Capsule (no good)
  4. Checked that the Time Capsule wasn’t restricting connections (it wasn’t)
  5. Updated the Time Capsule’s firmware to 7.6.4 from 7.6.1 (no good)
  6. Tried entering the wrong password to see whether I would get a different error message (I could not)

I was rather stumped, but I was getting closer. At least I was eliminating possibilities.

Sometimes in a case like this the problem involves the Keychain (where the computer’s passwords are stored). What happens is the password, which is supposed to be supplied automatically, somehow gets corrupted (or maybe the password’s been entered twice, once right and once wrong, and the Mac supplies the wrong one, by mistake). In that case, what we do is go to the Keychain Access application, find the key (or keys) that store the password for this particular network, and then delete it (them)– and then, with a clean slate, try to join the network one more time and very carefully type in the correct password. That’s what I did– but it didn’t solve the problem. So now I was even more stumped.

Keep in mind that the connection to a network is not a “user” property. Network connections belong to the machine, not to any particular user. Switching to another user on the same Mac wouldn’t have accomplished anything.

All of this led me to realize that the problem was in the MacBook Pro itself– not in the Time Capsule, not in the user, not in the Keychain. I figured the Airport card inside the MacBook Pro needed to be reset somehow. The question was “how.” The answer was “by resetting the SMC.” Now all you need to know is, what’s an SMC, and how do you reset it.

SMC = System Management Controller. It’s a subsystem inside modern Macs that, when malfunctioning, can make a lot of things break, including Airport wireless networking. (If your Mac’s USB devices aren’t recognized, or the fans seems to run overly fast, or the Mac doesn’t wake up reliably, that might be an SMC issue also.) The SMC’s settings are stored in non-volatile RAM, which means they’re stored on chips inside the Mac, not in a file in the Preferences folder the way many other settings are stored. Different machines require different reset procedures (see this link to Apple’s website), but this one needed only this:

Shut down MacBook Pro. Press Shift, Control, and Option on the left-hand side of the keyboard while simultaneously pressing the power button. (Nothing will happen.) Let go of everything– the keyboard, and the power button– all at once, then press the power button by itself one more time. Voilá, the SMC’s reset.

And guess what: after the SMC reset the MacBook Pro joined the network just fine, as if nothing had ever happened. A happy ending.

(You might think “I’ll just reset the SMC as my first trouble-shooting step and save a lot of time.” I wouldn’t do it that way. The SMC controls a lot of different things so there are lots of different settings in it. I blasted them out and got a nice, new, factory-condition set of settings– solving the immediate problem, but changing a lot of other settings that I didn’t really want to change. Nothing serious, just lots of little things, and no data loss or anything like that. Still, resetting the SMC is an all-or-nothing thing– you can’t reset just one part of it– and it could be inconvenient to the user to have so many settings changed at once.)

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