Mac computers: Sleep Indicator Light behavior
Note: If your MacBook, MacBook Air, and MacBook Pro has a SIL, the following behaviors will occur. These behaviors also occur on some iMac and Mac Pro models, although not all Macs have a SIL.
SIL states and behaviors
Power-On Self-Test (POST)
If the SIL flashes one or more times after you press the power button to turn on the computer, and the pattern repeats after a brief pause, the computer may not have successfully passed POST.
- If your computer encounters hardware issues during POST, the computer may use on a combination of audible tones and blinking SIL behavior to communicate POST issue codes.
- To determine the cause of a POST issue, observe the SIL blinking pattern. Then, refer to the following Apple support article for more information about POST codes: Intel-based Mac Power On Self Test RAM error codes.
When you press the power button to turn on the computer, the SIL will also turn on. As the computer starts up, the SIL stays on until the processor (GPU) has initialized and the display turns on. When the GPU initializes properly, the display will turn on and the SIL will turn off simultaneously.
- You can use the SIL as a diagnostic visual to determine whether the computer is getting power at startup.
- MacBook Air (Original, Late 2008, and Mid 2009) Battery Diagnostic: If the MacBook Air's SIL flashes five times at power on or after waking from sleep, and the pattern repeats after a brief pause, the computer's battery may require service. For more information, refer to MacBook Air (Original, Late 2008, and Mid 2009): About the battery diagnostic.