How to Start the Diagnostic Mode on a MacBook Pro

Remove any external peripherals from your Macbook Pro, such as mice, keyboards or monitors.
Restart the Mac laptop.
Press the 'D' key as your computer boots and continue holding it until you see a gray start screen.
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.'
Click 'Test.' All test results appear on your Macbook Pro's screen.
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