Apple Diagnostics can provide evidence about a suspected hardware issue. Its result is most useful when you keep the reference code together with the original symptom and the conditions under which you ran the test.

Prepare a controlled test

Save work and shut down. Apple's preparation guidance removes external devices except the keyboard, mouse, display, Ethernet connection where relevant and power. Put the Mac on a stable, ventilated surface.

Record any accessory you disconnected because the problem only appears when it is attached. The diagnostic result will then have a clear scope: it was obtained without that accessory in the chain.

On a Mac with Apple silicon, hold the power button to load startup options, release it when Options appears, then hold Command-D until the Mac restarts. On an Intel Mac, start up while holding D; Apple describes Option-D as an alternative when needed.

Follow the displayed test and keep the code

The sequence varies with hardware and software. Apple says macOS Tahoe 26 and later may ask you to choose a specific diagnostic, while earlier versions select tests automatically. Follow the actual prompts rather than assuming a screenshot from another release is identical.

Record the exact result and any reference code. Also record the Mac model, date and symptom that led you to test. Avoid including account passwords, recovery keys or unrelated personal information in a result screenshot.

A reported code is evidence for further assessment, not a complete quotation for replacement parts. Conversely, a test without a reported issue does not reproduce every intermittent fault, external-device problem or application behaviour you may encounter.

After the test, return to the normal setup and check the original task only if it is safe to do so. If the Mac is wet, physically damaged or showing signs of unsafe battery condition, seek assessment instead of repeatedly testing it. Provide the diagnostic result with your fault description.

Source: Apple Diagnostics preparation and test instructions.

For help with your Mac, contact AEPC in East Auckland or call 027 908 8880 to discuss your requirements.