How to run Apple Diagnostics on a Mac

2 min read · 6 steps · Updated 2 October 2026

Short answer

Shut down and unplug everything except power, keyboard, mouse and display. On Apple silicon, hold the power button until the startup options appear, then hold Command and D. On an Intel Mac, turn it on and hold the D key. The test shows a result with reference codes.

Apple Diagnostics is a test built into every Mac. It checks parts such as memory, battery, fans and the logic board. It helps you find out whether a problem is in the hardware before you pay for a repair.

The pictures are diagrams of the keys to press.

Step by step

  1. Prepare the Mac

    Install the latest macOS update if you can. Shut down. Disconnect all external devices except keyboard, mouse, display, a network cable if you use one, and power. Place the Mac on a hard, flat surface with good air flow.

  2. Apple silicon: hold the power button

    Press and hold the power button. Keep holding while the Mac turns on. Let go when the startup options appear, which show a gear icon called Options.

  3. Command+DApple silicon: start the test

    Apple silicon: hold Command and D

    Press and hold both keys until the Mac restarts into the test.

  4. DIntel: hold during startup

    Intel Mac: turn on and hold D

    Press the power button and immediately hold the D key. Let go when you see a progress bar or are asked to choose a language. If that does not work, try again while holding Option and D.

  5. Follow the instructions

    You may be asked to choose a language and a Wi-Fi network. On recent versions of macOS you can also choose which tests to run.

  6. Read the result

    When the test ends, the screen shows the result with one or more reference codes. Write the codes down. Apple lists what each code means on its support site.

Good to know

When you are done, restart or shut down the Mac.

A clean result does not prove that everything is fine. The test finds many hardware faults, but not all, and it does not check software.

A reference code tells a repair shop where to look. Take the code with you or quote it when you contact Apple Support.

If the Mac does not start at all, see Mac won't turn on: 7 things to try before a repair.

In short: Unplug extras. Apple silicon: hold power, then Command and D. Intel: hold D at startup. Note the reference codes.

Sources
  • Apple Support: Use Apple Diagnostics to test your Mac

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