I have problem with SMC in MacBook Air 2016. While running on battery, data from SMC module freezes. In iStat Menus temperatures from sensors, RPMs, current meters and voltage meters from CPU aren't refreshing. Also fan sometimes switches on high RPM and runs continuously, even when laptop is quite cold. When I plug in charger, fan goes back to 1200 RPM and temperatures are being normally refreshed. I had this issue propably even before updating to Mojave. I tried resetting SMC, but nothing happens. What is the possible reason for this issue?

  • so your iStat is not working ?
    – Ruskes
    Dec 27, 2018 at 22:22
  • iStat works, but problem is with SMC overall. Fan is working really strange, it's turning on when not necessary, and won't tun off until I connect power or turn system to sleep. Dec 28, 2018 at 14:21
  • so did you successfully reset SMC with visual confirmation ?
    – Ruskes
    Dec 28, 2018 at 16:52
  • When resetting SMC watch the MagSafe light briefly flicker.
    – Ruskes
    Dec 28, 2018 at 16:54
  • I did, and MagSafe turned green for a sec (battery was about 50% so it was orange normally) Dec 28, 2018 at 17:01

1 Answer 1


You've already reset the System Management Controller, which was the first thing to try, so I would probably start with testing to see if this behaviour is replicated when booted into Safe Mode and if the issue persists then running Apple Diagnostics.

Boot into Safe Mode

Follow these steps to boot your Mac into Safe Mode:

  1. Fully shut down your MBA
  2. Restart your MBA
  3. Immediately press the Shift key and keep it down
  4. Let go of the Shift key when you see the login window (NOTE: If you have FileVault enabled you may need to log in twice).
  5. Take a note of what happens (i.e. does your MBA still seem to behave strangely when running on battery, etc)
  6. Exit Safe Mode by restarting your MBA as normal
  7. Test again when booted normally

If the problem doesn't occur while booted into Safe Mode, let me know and we'll go from there.

If the problem persists, proceed with running Apple Diagnostics.

Run Apple Diagnostics

Follow the steps below to run Apple Diagnostics:

  1. Fully shut down your MBA
  2. Restart your MBA
  3. Immediately press the D key and keep it down until you see the Diagnostics screen appear
  4. Wait for Diagnostics to finish (this typically only takes a few minutes)
  5. Once complete, one of two things will appear on the screen:
    • a No issues found message
    • a brief description of any errors found plus further instructions
  6. If the diagnostics test does find errors, take a note of what they are

Note: If pressing and holding the D key at Step 3 doesn't work, start again at Step 1 and, at Step 3 press and hold both the OptionD keys instead. This will try and run diagnostics from the internet instead, so you will need to allow more time for it to complete.

Regardless, take a note of what happens and let me know how you went.

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