Code 404: SERVO ALARM: n–TH AXIS VRDY ON
Issue Description & Safety Warning
The Fanuc 16i/18i/21i CNC has triggered a critical SERVO ALARM: n–TH AXIS VRDY ON alarm. Immediate attention from a qualified operator or maintenance technician is required to prevent secondary damage to the equipment or spoiled parts during the manufacturing cycle. Always ensure standard safety and LOTO procedures are followed before accessing electrical cabinets.
Official Troubleshooting Steps
Even though the n–th axis (axis 1–3) READY signal (MCON) went off, the servo amplifier READY signal (DRDY) is still on. Or, when the power was turned on, DRDY went on even though MCON was off. Check that the servo interface module and servo amp are connected.
Source: Fanuc Series 16i/18i/21i-B Operator's Manual, Appendix G Alarm List (B-63864EN/03)
Last reviewed: 2026-07-01 · Verified against the manufacturer’s official documentation.
About Fanuc 16i/18i/21i CNC Alarms
Fanuc controllers include extensive self-diagnostics that flag or halt the machine when a fault is detected. Error code 404 on the 16i/18i/21i CNC identifies one specific fault condition — its documented cause and the official corrective steps are listed above, sourced from Fanuc's service documentation. Always confirm against the manual for your exact machine configuration and follow LOTO procedures before servicing.
Complete Alarm List: 360 Fanuc 16i/18i/21i CNC codes.
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