What Does Resetting the Intel Mac’s System Management Controller (SMC) do?

Sometimes a Mac behaves erratically. When it refuses to turn on, wake up from sleep mode, doesn’t recognize the AC adapter, or doesn’t charge the battery it could be a hardware problem. Or it could be that the Mac’s power manager (The SMC) became corrupted and unusable. A quick fix to try before taking your MacBook/MacBook Pro into the Apple repair center is to reset the power manager. In this article, I’ll explain what the SMC does and how to reset it.

What does the System Management Controller (SMC) do?

Knowing what the SMC controls will help you determine if resetting it will solve a problem you are having. The System Management Controller (SMC) is a chip on your Mac’s logic board that deals with the following tasks:

- Power management of the computer.
- Controlling the display’s backlight.
- Hard drive spin-down and activation.
- Sleep mode and waking up from sleep mode.
- Parts of the battery charging process.
- Controlling the Trackpad.
- Input/Output related to sleep mode (Airport turning on/off, USB, FireWire)

Note: The SMC chip is only a part of Intel-based Macs. For the PowerPC platform, a similar chip is called the Power Management Unit (PMU). While similar in function, resetting the PMU is a completely different process.

When should I try resetting the SMC?

Resetting the SMC is a valid “Quick Fix” for the following problems:

- Your Mac won’t turn on.
- Your Mac will not wake up from sleep mode.
- A/C adapter is not recognized.
- The Battery won’t charge.
- Trackpad becomes unusable for no apparent reason.
- Wireless won’t work after waking from sleep-mode.

Basically, any problem dealing with power management would warrant an SMC reset as a quick fix. Obviously if you dropped it or spilled liquids all over the computer and it doesn’t turn on anymore, the SMC reset won’t help.

Note: An SMC reset is not for when the computer doesn’t respond or freezes. (Spinning beach ball / color wheel)

Resetting the SMC on a MacBook or MacBook Pro:

1. Turn off the computer.
2. Remove the battery and unplug the A/C adapter.
3. Press and hold the power button for five seconds and then release the button.
4. Reconnect the battery and A/C adapter.
5. Start up the computer.

Resetting the SMC on a MacBook Air:

1. Turn off the computer.
2. Plug in and connect the A/C adapter.
3. Press the Left Shift key, Control key, Option key and the power button at the same time, just once.
4. Wait five seconds.
5. Start up the computer.

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7 Comments

  1. jeanette says:

    Will a SMC reset cause my MAC to lose files or data? Is it completely safe? Thanks!!!

    I am planning to do one as my MAC won’t accept disks…automatically rejects them.

    Jeanette

  2. David Balogh says:

    Hi Jeanette,

    As long as you shut down your Mac properly (By choosing Shut Down from the Apple Menu and waiting for it to turn off), resetting the SMC is safe for your data.

    If your Mac is rejecting discs (they go in, spin for a bit and then it spits them back out) try another disc. If that one plays, it might be the disc.

    However if all of your known good discs don’t play, it might need to be repaired.

    Good Luck,
    David

  3. Sarah says:

    Hi David,
    My computer was in sleep mode and wouldn’t turn on so I did an SMC reset. It worked but now my adapter is not being recognized and the battery is dead. Is there something I can do to fix this or do I need to take it in?

    Thanks,
    Sarah

  4. David Balogh says:

    Hi Sarah,

    Sounds like your MacBook is having some power issues. It could be one of three things:

    - The battery. (About $100 for a new one)
    - The adapter. (About $80 for a new one)
    - The MacBook’s internal parts. (Free if it’s warranty / Apple Care covered, expensive if not)

    I’d recommend taking it in, as the Apple Service Center will have spare batteries and adapters to test with. Before you do, try the following:

    1. Check and make sure it’s plugged in and the outlet is good.
    2. If you are using the extended cord, make sure it is firmly attached to the adapter.
    3. Check where you plug in the adapter on the computer – make sure it attaches properly.
    4. Look for staples or other small metal objects that may get magnetically stuck in there and keep the adapter from working.
    5. Check if there’s a Green / orange light on the side.
    6. If the light goes on, take out the battery and see if the MacBook will turn on with only the adapter to power it.

    If it runs without the battery, the adapter isn’t the problem. If it doesn’t – try another adapter. If it still doesn’t even with a known good adapter, it’s most likely the internal components.

    Good Luck,
    David

  5. Ryan says:

    Hi David,

    My Macbook has been having problems getting wireless signal. It sometimes gets it for a while and it works fine, but then it will suddenly disconnect. We have another mac in the house that doesn’t lose signal.

    I reset the SMC but it didn’t help the problems.

    Any ideas?

    Thanks in advance

  6. David Balogh says:

    Hi Ryan,

    Wireless problems can be tricky especially when they are intermittent. Since it seems to be specific to one computer, I’d look at factors like:

    - How far the computer is from the AP.
    - Does the other computer have problems in the same area as the MacBook?
    - Are there many other APs nearby that could interfere? (Apartment building, close neighbors, etc)
    - Are there sources of interference like cordless phones, microwaves and other 2.4Ghz devices?

    If none of these apply, I’d begin looking at the laptop itself. Try booting from the OS X install DVD and see if the airport functions appropriately. If not, you may need either the antennae or airport card replaced.

    Good Luck,
    David

  7. anne says:

    When resetting the SMC .. does the computer need to have some kind of power?? my macbook won’t recognize the battery .. there’s an X over the battery icon .. and the LED light on the adapter is always green .. I can’t turn it on without the adapter.