Fanuc alarm 403: S-BUS TIMEOUT ERROR
30i/31i/32i system alarm · Fanuc 30i/31i/32i-B
What it means
A timeout occurred on the S-Bus used for communication between processors on the 30i multi-CPU system. Fanuc attributes this to a problem on the CNC bus, most often the main board or the MASTER/SLAVE PCB shown on screen. On machines linked to a PC by HSSB, a PC restart, hang or aggressive power-management standby can also trigger this timeout.
Likely causes
- Main board or sub-CPU board fault
- HSSB-connected PC restarting or entering standby mode
- External noise affecting the bus
Need the part urgently?
Send us alarm 403 with your machine details — typical RFQ turnaround is 24–48h.