Fanuc alarm 921: SERVO ALARM (5-8 AXIS)
system alarm · Fanuc 0i-D
What it means
A watchdog timeout occurred, or a RAM parity error was detected, on the axis-control LSI/card serving axes 5 through 8. Functionally identical to alarm 920 (axes 1-4) but pointing at the second servo interface section of the control hardware.
Likely causes
- Faulty axis control card / servo interface LSI
- Servo amplifier or FSSB side fault pulling down the axis section
- Noise-induced watchdog trip
Triage note: Only raised on systems configured with more than four axes.
Need the part urgently?
Send us alarm 921 with your machine details — typical RFQ turnaround is 24–48h.