When you’re having trouble with your Mac, one suggestion you hear a lot is to reset the System Management Controller, or SMC. Is that actually a helpful step to take? What actually happens when you perform the reset? Let’s find out.

What’s the SMC Do?

Your Mac’s SMC controls many low-level functions of the computer. According to Apple, that includes all of the following, and more:

  • Responding to presses of the power button
  • Responding to the display lid opening and closing on Mac notebooks
  • Battery management
  • Thermal management
  • Sudden Motion Sensor (SMS)
  • Ambient light sensing
  • Keyboard backlighting
  • Status indicator light (SIL) management
  • Battery status indicator lights
  • Selecting an external (instead of internal) video source for some iMac displays

Is it always useful to reset the SMC? Not really, but there are plenty of scenarios where it can save the day. Here’s a list of a few:

  • Your computer’s fans run at high speed, even though it isn’t under heavy usage and is properly ventilated.
  • The keyboard backlight behaves incorrectly.
  • The status indicator light, if present, behaves incorrectly.
  • Battery indicator lights, if present, behave incorrectly on Mac notebooks with a non-removable battery.
  • The display backlight doesn’t respond correctly to ambient light changes.
  • Your Mac doesn’t respond when you press the power button.
  • Your Mac notebook doesn’t respond properly when you close or open the lid.
  • Your Mac sleeps or shuts down unexpectedly and you can’t turn it back on.
  • The battery doesn’t charge properly.
  • Your MacBook or MacBook Pro doesn’t charge through its built-in USB-C port.
  • Your MacBook or MacBook Pro doesn’t recognize external devices that are connected to its built-in USB-C port.
  • The MagSafe power adapter LED, if present, doesn’t indicate the correct charging activity.
  • Your Mac performs unusually slowly, even though its CPU isn’t under an abnormally heavy load.
  • A Mac that supports target display mode doesn’t switch into or out of target display mode as expected, or it switches into or out of target display mode at unexpected times.
  • The illumination around the I/O ports on a Mac Pro (Late 2013) doesn’t turn on when you move the computer.

Before resetting the SMC, it’s always a good idea to restart your Mac normally. Sometimes simply turning the computer off and on again will resolve similar issues, but if not, here’s how to go ahead with the next step.

Resetting On A Notebook

The first thing to find out when dealing with a MacBook, MacBook Air, or MacBook Pro is whether the battery is removable. Most older notebooks have removable batteries, but nonremovable batteries are found on MacBook Pro Early 2009 and later, all models of MacBook Air, MacBook Late 2009, and MacBook Retina, 12-inch, Early 2015 and later. These days, most people are using the nonremovable variety. If that’s the case, follow these steps:

  • Choose Apple menu > Shut Down.
  • After your Mac shuts down, press Shift-Control-Option on the left side of the built-in keyboard, then press the power button at the same time. Hold these keys and the power button for 10 seconds. (If you have a MacBook Pro with Touch ID, the Touch ID button is also the power button.)
  • Release all keys.
  • Press the power button again to turn on your Mac.

Got an older Mac notebook with a removable battery? The steps differ just a bit.

  • Shut down your Mac.
  • Remove the battery. If you need help removing the battery, contact an Apple Authorized Service Provider or Apple Retail Store.
  • Press and hold the power button for 5 seconds.
  • Reinstall the battery.
  • Press the power button again to turn on your Mac.

Resetting On A Desktop

For you desktop owners, the process is always the same with one exception: the iMac Pro. So if you have an iMac, Mac mini, Mac Pro, or Xserve, follow these steps:

  • Choose Apple menu > Shut Down.
  • After your Mac shuts down, unplug the power cord.
  • Wait 15 seconds.
  • Plug the power cord back in.
  • Wait 5 seconds, then press the power button again to turn on your Mac.

The iMac Pro is even simpler, there’s no unplugging of a power cord necessary:

  • Choose Apple menu > Shut Down.
  • After your iMac Pro shuts down, press and hold its power button for 8 seconds.
  • Release the power button, then wait a few seconds.
  • Press the power button again to turn on your iMac Pro.

And now you know! So the next time your Mac’s fan starts spinning out of control, you’ve got the tools to combat it. This doesn’t cover the whole spectrum of Mac troubleshooting, certainly, but it’s one of the most common suggestions you’ll hear, and you’ll never have to bother looking it up again.