Asus P9D-C/4L - Manual (Page 43)

ASUS P9D-C Series 2-23
2. Baseboard Management Controller LED (BMC_LED1)
The green heartbeat LED blinks per second to indicate that the ASMB7 is working
normally.
The heartbeat LED functions only when you install the ASUS ASMB7.
2.6 Onboard LEDs
1. Standby Power LED (SB_PWR1)
The motherboard comes with a standby power LED. The green LED lights up to
indicate that the system is ON, in sleep mode, or in soft-off mode. This is a reminder
that you should shut down the system and unplug the power cable before removing or
plugging in any motherboard component. The illustration below shows the location of
the onboard LED.