Asus Z8PE-D18 - Motherboard - SSI EEB 3.61 User Manual page 22

2. CPU warning LED (ERR_CPU1, ERR_CPU2)
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 ASMB4.
3. DIMM warning LED (ERR_DIMMA1/2; ERR_DIMMB1/2; ERR_DIMMC1/2;
ERR_DIMMD1/2; ERR_DIMME1/2; ERR_DIMMF1/2)
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.
2-4 Chapter 2: Hardware information