PowerOn Self Test POST Error Codes

The computer automatically performs a power-on self test when it is turned on after being fully shut down (not a restart). This section describes what to do if you hear beeps during startup. When this occurs, the sleep LED will stay on, occasionally flashing.

MacBook Pro relies on a combination of tones and blinking sleep LEDs to display power-on self test (POST) error codes.

If the computer detects no SDRAM (Synchronous Dynamic Random Access Memory—also referred to as RAM), or the RAM installed does not meet the appropriate specifications, the screen will remain black but the power LED on the front of the computer will blink once per second to signal the error. This error condition may be due to physically damaged RAM, the incorrect type of RAM, or not having any RAM installed.

Some RAM may appear to pass the power-on self test (POST) but still cannot be addressed by the operating system. In this case, the computer will display a gray screen, sound three tones and blink the power LED on the front of the computer three times, pause, and repeat the blinking until the computer is turned off.

Related Knowledge Base articles:

303083: Intel-based Mac Power On Self Test RAM error codes 303363: Intel-based Mac: Startup sequence and error codes, symbols

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