Asus Z9NA-D6 - Manual (Page 40)

2-20 Chapter 2: Hardware information
2.6 Onboard LEDs
1. Baseboard Management Controller LED (BMC_LED1)
The BMC LED works with the ASUS ASMB6 management device and indicates
its initiation status. When the PSU is plugged and the system is OFF, ASUS
ASMB6 management device starts system initiation for about one (1) minute.
The BMC LED blinks after system initiation finishes.
2. CPU warning LED (ERR_CPU1/2)
The CPU warning LEDs light up to indicate that an impending failure of the
corresponding CPU.
The warning LEDs function only when you install the ASUS ASMB6.