How to Start the Diagnostic Mode on a MacBook Pro

Intel-based Macs, such as the Macbook Pro, have a diagnostic mode that checks the computer's hardware components for any signs of failure. You can use the diagnostic mode to check your hardware and eliminate it as a cause of problems if your system is exhibiting problematic behavior. Depending on your needs, select basic or more extensive testing.

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Remove any external peripherals from your Macbook Pro, such as mice, keyboards or monitors.

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Restart the Mac laptop.

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Press the "D" key as your computer boots and continue holding it until you see a gray start screen.

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Choose your language and press right. Select the basic test battery by pressing "T" or perform the more extensive hardware test by checking "Perform extended testing."

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Click "Test." All test results appear on your Macbook Pro's screen.