Asus KCMA-D8 - Manual (Page 22)

2-4 Chapter 2: Hardware information
2. CPU warning LED (ERR_CPU1, ERR_CPU2)
The CPU warning LEDs light up to indicate that an impending failure of the
corresponding CPU.
3. DIMM warning LED (ERR_DIMMA1/2; ERR_DIMMB1/2; ERR_DIMMC1/2;
ERR_DIMMD1/2)
The DIMM warning LEDs light up to indicate that an impending failure of the
corresponding DIMMs.
The warning LEDs function only when you install the ASUS ASMB4.
The warning LEDs function only when you install the ASUS ASMB4.