There are three reasons the axis FAULT LED's will illuminate on the 4000 Front Panel:
1. Axis has been shut down via the SHTDN command. Only the affected axis will be illuminated.
2. A hard limit has been hit or is disconnected. Only the affected axis will be illuminated.
===> note: Be sure to use ENABLE HLIMIT to disable checking of unused limits.
3. E-STOP input is not connected. All axes fault LED's will be illuminated.