Using Apple Hardware Test
- Shut down your computer. Then, press the power button to turn it back on.
- Press and hold the D key before the gray startup screen appears.
- It takes a minute or so for AHT to start up and inspect your hardware configuration. While this is taking place, an icon appears on the screen:
- When the process is complete, select your language and click the right arrow. If you aren't using a mouse, you can use the up and down arrows to select a language and then press the Return key.
- The AHT console appears. You can choose which sort of test or tests to perform:
- To perform all of the basic tests, click the Test button or press the "T" key or the Return key.
- To perform a more thorough diagnostic test, select the "Perform extended testing" checkbox under the Test button before you click the Test button.
Note: Your test results will appear in the window in the bottom-right of the console.
- To exit AHT, click Restart or Shut Down at the bottom of the window.
Some Macintosh computers that shipped with OS X Lion and later support the use of Apple Hardware Test over the Internet. These computers will start up to an Internet-based version of AHT if the hard drive does not contain AHT. An Internet-enabled connection via Ethernet or Wi-Fi is required to use this feature. Internet-based AHT functions the same as AHT on the hard drive or flash storage outlined above.