Fanuc alarm SV0404: IMPROPER V_READY ON
αi/βi Servo (SV0xxx) · Fanuc 0i-D
What it means
The velocity-control ready signal (VRDY) came ON while the CNC-side position ready signal (PRDY) was still OFF — the mirror image of SV0401. The amplifier asserted readiness without being commanded, indicating the amplifier's control board is latching abnormally or the ready-signal handshake path is faulty. Power-cycle to test; recurrence implicates the servo amplifier's interface section.
Likely causes
- Servo amplifier control board fault
- Abnormal sequence at power-up (amplifier ready before CNC)
- Wiring/contact fault in the PRDY/VRDY handshake circuit
Need the part urgently?
Send us alarm SV0404 with your machine details — typical RFQ turnaround is 24–48h.