The System Management Controller is an integrated circuit (computer chip) that is on the logic board of the computer. As the name implies, it is responsible for power management of the computer. It controls backlighting, hard disk spin down, sleep and wake, some charging aspects, trackpad control, and some input/output as it relates to the computer sleeping.
Over time, the settings in the System Management Controller may become unusable, which can result in operational anomalies with the computer. Examples include not turning on, not waking from sleep, not charging the battery, or not recognizing the AC Adapter, among others.
Resetting the SMC is not intended for resolution of a stall or situation in which the computer is unresponsive. An SMC reset should not be necessary except as a last resort in cases where a hardware issue with the power management system is suspected. Performing an SMC reset resets the hardware power management functions.
For most situations, a restart is sufficient. If the computer has stopped responding, try each one of these steps, one by one. Test between each step to see if it has worked. If one step works, don't worry about the next one. You should only reset the SMC if you've tried all of the steps listed here and the computer still isn't working.
- Force Quit (Option-Command-Escape)
- Restart (Control-Command-Power)
- Force Shut Down (press the power button for 10 seconds)
Only perform an SMC reset on the computer if none of the above steps resolved the situation. If this is the case, see below for instructions on locating the reset button or key combination for your model of computer. If your computer is earlier than the models listed here, see "Resetting PowerBook and iBook Power Management Unit (PMU)" or "PowerBook: Resetting Power Management Unit (PMU)".
MacBook (13 inch, Late 2008), MacBook Pro (15-inch, Early 2008), and MacBook Pro (17-inch, Early 2008)
- If the computer is on, turn it off.
- Disconnect the AC adapter and remove the computer's battery.
- Press and hold the power button for 5 seconds and then release the button.
- Reconnect the battery and AC Adapter.
- Press the power button to restart the computer
Note: Starting with MacBook Pro (Late 2008) and MacBook (Late 2008) models, you may instead use the reset method for MacBook Air (below) to reset the SMC. All earlier models of MacBook and MacBook Pro must use the method described above, which involves removing the battery.
MacBook Air and MacBook Pro (Late 2008 and later)
- If the computer is on, turn it off by choosing Shutdown from the Apple () menu.
- Connect the power adapter to a working power source.
- On the built-in keyboard, press (left) Shift-Control-Option along with the power button once.
- Wait 5 seconds and press the power button to start the computer.
Note: You must use the keys on the left side of the built-in keyboard.
You should only perform an SMC reset when the MacBook Air or MacBook Pro (17-inch, Early 2009) has been properly shutdown. This prevents issues from occurring to the file system.
While the power adapter does not need to be connected to reset the SMC, it may be necessary in situations where the battery needs charging or if the computer has been without power for an extended period of time. You can also visually check the SMC reset by observing the LED on the adapter. It will momentarily turn off as the SMC resets.
