Fanuc alarm SV0487: ILLEGAL SAFETY MODE (CNC)
safety/dual-check alarm · Fanuc 30i/31i/32i-B
What it means
The CNC side detected that safety signal mode D was reached although no guard open request had been input, or the guard is open while the unlock signal *LGD is inactive. It mirrors SV0480 but as seen from the CNC CPU channel of the cross-check. Fanuc advises verifying the guard state signal (SGD) wiring first; the alarm may also appear legitimately if unlocking is disabled in mode C.
Likely causes
- Guard state signal (SGD) miswired, faulty or chattering
- Door opened without ORQ (guard open request) sequence completing
- PMC logic outputting *LGD incorrectly relative to actual door state
Need the part urgently?
Send us alarm SV0487 with your machine details — typical RFQ turnaround is 24–48h.