Asus P9D-I - Manual (Page 38)

2-18 Chapter 2: Hardware information
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.
2. CPU Warning LED (ERR_CPU1)
The CPU warning LED lights up to indicate that a CPU error or failure has occurred.
The warning LED functions only when you install the ASUS ASMB7 Management card.