LogrobotLM

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FANUC Alarm PRIO-494 — Modbus Active Close

FANUC PRIO-494 (“Modbus Active Close”): 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. First check: Increase the number of connections using the Modbus TCP screen.

Updated 2026-09-17 · LogrobotLM reference

Description

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.

Related codes

PRIO-490Modbus TCP Server ErrorPRIO-493Modbus Socket ErrorPRIO-495Modbus TimeoutPRIO-499Modbus System Error

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