Apple Diagnostic Mode

  1. Disconnect all external devices except keyboard, mouse, display, Ethernet connection (if applicable), and connection to AC power.
  2. Shut down your Mac.
  3. Turn on your Mac, then immediately press and hold the D key on your keyboard. Keep holding until you see a screen asking you to choose your language. When Apple Diagnostics knows your language, it displays a progress bar indicating that it's checking your Mac.
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