Code PRIO-494: Modbus Active Close
Issue Description & Safety Warning
The Fanuc R-30i Series Robot Controller has triggered a critical Modbus Active Close 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
Cause: A Modbus TCP master device is trying to establish a connection with the robot Modbus slave, but the server is already using all available connections. This is a warning alarm and will only be posted the first time this happens after each power-cycle. Per the Modbus TCP protocol, when a new connection request arrives and there are no unused connections, the oldest connection will be closed, and the new connection request will be accepted. Remedy: Increase the number of connections using the Modbus TCP screen.
Source: FANUC Robot R-30iA Alarm Code List Operator's Manual
Last reviewed: 2026-07-01 · Verified against the manufacturer’s official documentation.
About Fanuc R-30i Series Robot Controller Alarms
Fanuc controllers include extensive self-diagnostics that flag or halt the machine when a fault is detected. Error code PRIO-494 on the R-30i Series Robot Controller 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: 6553 Fanuc R-30i Series Robot Controller codes.
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