Fanuc alarm SV0491: LOCAL BUS TEST ERROR
safety/dual-check alarm · Fanuc 30i/31i/32i-B
What it means
The periodic local-bus test inside the safety system failed, indicating the motherboard bus carrying cross-check traffic between the CNC CPU and monitor functions is faulty. Fanuc states the mother board may be defective and should be replaced. Immediate stop is applied since safety redundancy is in doubt.
Likely causes
- Motherboard failure
- Bus noise or poor board seating
Replacement parts
We supply the following units for this alarm — tested, warranty-backed:
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Mother board
board · Common cause
Need the part urgently?
Send us alarm SV0491 with your machine details — typical RFQ turnaround is 24–48h.