The SMC (System Management Controller) controls a number of the Mac's core functions. The SMC is a piece of hardware incorporated into the Mac's motherboard. Its purpose is to free the Mac's processor from having to actively take care of rudimentary hardware functions. With so many core tasks performed by the SMC, it is no wonder that resetting the SMC to its default state can fix so many issues.
What the SMC Controls
Depending on your Mac model, the SMC performs the following functions:
- Responds to the press of the power button, including deciding whether the press is for a power off, sleep, or an accidental misstep by your cat.
- Detects and responds to the opening or closing of the lid of a portable Mac.
- Manages a portable's battery performance, including charging, calibration, and displaying remaining battery time.
- Thermal management of your Mac's interior. This is primarily accomplished by sensing temperature at various places inside your Mac, and then adjusting fan speed to create or reduce airflow.
- Uses the SMS (Sudden Motion Sensor) to respond to the sudden motion of a Mac portable and acts to prevent damage to various devices.
- Detects ambient lighting conditions and sets appropriate lighting levels for various devices.
- Controls keyboard backlighting.
- Controls built-in display backlighting
- Controls SILs (Status Indicator Lights) that are present on or in your Mac.
- Selects external or internal video sources (primarily for iMacs with video input capabilities).
- Starts hard drive spin downs, as well as power up sequences.
- Controls sleep mode functions (waking and entering sleep).
- Controls trackpad functions for some Mac models.
Signs You Need to Reset the SMC
Resetting the SMC is not a cure-all, but there are many symptoms a Mac may suffer from that a simple SMC reset can fix.
These include:
- Erratic sleep mode performance, including not waking from or not entering sleep.
- Your Mac entering sleep unexpectedly, even while actively working on it.
- Mac portables (MacBook, MacBook Pro, MacBook Air) not responding to lid opening or closing.
- Failure to respond to the power button being pressed.
- MagSafe power indicator not displaying or displaying incorrectly.
- Sluggish performance, even though Activity Monitor shows little CPU usage.
- Target Display Mode not working correctly.
- Battery not charging or taking excessive time to charge.
- USB ports not working.
- Wi-Fi hardware reported as missing or not working.
- Bluetooth not working.
- Fans running fast.
- Display backlight not responding to ambient light level changes.
- SIL (Status Indicaor Lights) are not working correctly. They may be stuck in a static state.
- Bouncing Dock icons that seem to keep bouncing without the associated app launching.
- Mac Pro (2013) port illumination fails to turn on or off.
How to Reset Your Mac's SMC
The method for resetting your Mac's SMC depends on the type of Mac you have. All SMC reset instructions require shutting down your Mac first. If your Mac fails to shut down, try pressing and holding the power button until the Mac shuts down, which usually takes 10 seconds or so.
Mac portables with user-removable batteries (MacBook and older MacBook Pros):
- Shut down your Mac.
- Disconnect your Mac portable from its MagSafe connector.
- Remove the battery.
- Press and hold the power button for at least 5 seconds.
- Release the power button.
- Re-install the battery.
- Reconnect the MagSafe connector.
- Turn your Mac on.
Mac portables with non-user-removable batteries (MacBook Air, 2012 and later MacBook Pro models, 2015 and later MacBook models):
- Shut down your Mac.
- Connect the MagSafe power adapter to your Mac and to a power outlet.
- On the built-in keyboard (this will not work from an external keyboard), simultaneously press and hold the left shift, control, and option keys while you press the power button for at least 10 seconds. Release all keys at the same time.
- Press the power button to start your Mac.
Mac desktops (Mac Pro, iMac, Mac mini):
- Shut down your Mac.
- Unplug your Mac's power cord.
- Press and hold the Mac's power button for 15 seconds.
- Release the power button.
- Reconnect your Mac's power cord.
- Wait five seconds.
- Start your Mac by pressing the power button.
Alternative SMC reset for Mac Pro (2012 and earlier):
If you have a 2012 or earlier Mac Pro that isn't responding to the normal SMC reset as described above, you can force a manual SMC reset by using the SMC reset button located on the Mac Pro's motherboard.
- Shut down your Mac.
- Unplug the Mac's power cord.
- Open the Mac Pro's side access panel.
- Just below the Drive 4 sled and adjacent to the top PCI-e slot is a small button labeled SMC. Press and hold this button for 10 seconds.
- Close the Mac Pro's side door.
- Reconnect your Mac's power cord.
- Wait five seconds.
- Start your Mac by pressing the power button.
Now that you have reset the SMC on your Mac, it should be back to operating as you expect. If the SMC reset didn't fix your problems, you can try combining it with a PRAM reset. Although the PRAM works differently than the SMC, it can, depending on your Mac model, store a few bits of information that the SMC uses.
If you're still having issues, you may wish to try running the Apple Hardware Test to rule out a defective component on your Mac.
Cylindrical Mac Pro
An SMC reset is performed using the same method as 2012 and earlier Mac Pros. However, Apple has issued an SMC firmware update that should be installed in all 2013 and later Mac Pros.
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