SV0401Servo alarm · CNC servo monitoring
Fanuc αi SV0401: V Ready Off
Also shown as: 16i/18i/21i/0i: 401
What SV0401 means
The servo amplifier did not report ready (V READY OFF) when the CNC expected it.
Symptoms
Alarm at power-on or when coming out of emergency stop.
Is it repairable?
Repairable when an amplifier or PSM is at fault; often wiring or E-stop related.
Common causes
- Emergency stop chain open
- MCC contactor not closing
- PSM not ready or alarmed
- Another amplifier alarm
Safe checks
- 1Check the amplifier displays for alarm codes
- 2Check the E-stop chain and MCC contactor
Drives hold dangerous voltage after power-off. Checks should only be done by qualified personnel, with power isolated and the DC link discharged.
Reviewed by AutomIQ repair technicians. Code and name from the FANUC αi series Maintenance Manual.
Related Fanuc αi faults
- SV0368Serial data error (built-in)
- SV0433DC link undervoltage
- SV0436Soft thermal (OVC)
- SV0438motor current alarm
- SV0442DC link precharge failure
- SV0443cooling fan stopped