Functions Controlled by SMC
The list of functions controlled by the SMC is long and varies depending on the Mac model. The SMC performs the following functions:
Responds to the press of the power button, including deciding whether the press is for power-off or sleep, or was a 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 the remaining battery time. Handles the thermal management of the Mac’s interior by sensing the temperature inside the Mac and adjusting the fan speed to generate or reduce airflow. Uses the Sudden Motion Sensor to respond to the sudden motion of a Mac laptop and acts to prevent damage. Detects ambient lighting conditions and sets appropriate lighting levels for devices. Controls keyboard backlighting. Controls built-in display backlighting. Controls the status indicator lights. Selects external or internal video sources on iMacs with video input capabilities. Starts hard drive spin-downs and power-up sequences. Controls sleep mode functions. Controls trackpad functions for Mac models with trackpads.
Signs You Need to Reset the SMC
Resetting the SMC is not a cure-all, but it fixes many symptoms a Mac may suffer from, including:
Erratic sleep mode performance, including not waking from or not entering sleep. Entering sleep unexpectedly, even while you are actively working. Mac laptops that don’t respond to the lid opening or closing. Failure to respond to the power button being pressed. The power indicator doesn’t display or displays incorrectly. Sluggish performance, even when the Activity Monitor shows little CPU usage. Target Display Mode doesn’t work correctly. The battery isn’t charging or takes excessive time to charge. USB ports aren’t working. Wi-Fi hardware is reported as missing or not working. Bluetooth isn’t working. Fans run too rapidly. The display backlight doesn’t respond to ambient light-level changes. The status indicator lights don’t work correctly or are stuck in a static state. Bouncing Dock icons 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
If you experience any of these symptoms with your Mac, resetting the SMC may be the fix you need. The method for resetting a 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, press and hold the power button until the Mac shuts down, which usually takes 10 seconds or so.
Reset the SMC on Mac Notebooks With Nonremovable Batteries
All MacBook Air models have nonremovable batteries. So do MacBook and MacBook Pro models that were introduced in mid-2009 until the present, except for the 13-inch mid-2009 MacBook. This method is not recommended for Macs with the Apple T2 security chip introduced in 2018. To reset the SMC:
Reset the SMC on Mac Notebooks With Removable Batteries
Apple laptops with removable batteries include the 13-inch, mid-2009 MacBook, and all MacBooks and MacBook Pros introduced in early 2009 and before.
Reset the SMC on Mac Notebooks With the T2 Chip
The MacBook Air and MacBook Pro introduced in 2018 and later contain the Apple T2 chip. To reset the SMC on these notebooks: If your notebook computer problem continues:
Reset the SMC on Mac Desktops With the T2 Chip
If you have an iMac Pro or Mac Mini from 2018 or later or a Mac Pro from 2019 or later, it has an Apple T2 chip. You can confirm this in About This Mac in the Apple menu. To reset these desktop Macs:
Reset the SMC on Other Mac Desktops
The desktop computers that don’t have the T2 chip, which is most of the ones made before 2018, include Mac Pro, iMac, and Mac mini. To reset the SMC on these devices:
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, force a manual SMC reset by using the SMC reset button located on the Mac Pro’s motherboard. 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 the problem, combine it with a PRAM reset. Although the PRAM works differently from the SMC, it stores a few bits of information that the SMC uses. If you still have problems, run the Apple Hardware Test to rule out a defective component on your Mac.
