Asus RS740-E7-RS24-EG - Manual (Page 84)

Chapter 4: Motherboard information 4-20
8. Q-Code LEDs
The Q-Code LED provides you a 2-digit display that shows the system status. Refer to
the following Q-Code table more details.
7. CATT LED (CATTERR_LED1)
The CATT LED indicates that the system has experienced a fatal or catastrophic error
and cannot continue to operate.