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 2026-08-29 · 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 · Remède
Increase the number of connections using the Modbus TCP screen.
Frequently asked · Questions fréquentes
- What does FANUC alarm PRIO-494 mean?
- 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. This is a warning alarm and will only be posted the first time this happens after each power-cycle. Per the Modbus TCP…
- How do you troubleshoot FANUC alarm PRIO-494?
- Increase the number of connections using the Modbus TCP screen.
Related codes / Codes liés
Indicative field information — the robot manufacturer's manual and safety procedures always prevail. Never bypass a safety device; apply lockout/tagout (LOTO) before any physical intervention. · Informations indicatives issues du terrain — le manuel du constructeur et ses procédures de sécurité font foi. Ne shuntez jamais un organe de sécurité ; consignez (LOTO) avant toute intervention physique. How this reference is built →