Allen-Bradley EtherNet/IP Adapter Fault (1756-EN2T / 1756-EN2TR)

ControlLogix EtherNet/IP communication module has faulted or lost connections. Remote I/O racks, VFDs, and network devices connected through this module are offline.

Probable Causes (ranked)

• Module not fully seated in the ControlLogix chassis backplane
• Ethernet port link lost — cable disconnected, switch port down, or cable damaged
• Module IP address conflict — another device on the network has the same IP
• Module connection table full — too many CIP connections configured through this module
• Module firmware crash — needs power cycle to recover
• DLR (Device Level Ring) break detected on 1756-EN2TR — ring topology has an open segment

Fix Steps

1. 1 Check module front panel LEDs — Network Status (NS) should be green, Module Status (MS) should be green
2. 2 Check Ethernet cable connections at both ports — verify link LEDs on module and switch
3. 3 Reseat the module in the chassis if MS LED is off or red
4. 4 Verify IP address using module rotary switches or RSLinx — check for conflicts on the network
5. 5 Power cycle the module by removing and re-inserting it — allows firmware to restart
6. 6 If using DLR ring topology on EN2TR, check ring status — one cable break is OK (ring becomes linear), two breaks cause isolation
7. 7 Check connection count in module diagnostics — reduce connections or distribute across multiple EN2T modules if at limit

Suggested Replacement Parts

Parts matched to fault category: Network Module

Prices are estimates. Verify part numbers match your equipment before ordering.

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