What causes fault code AB-COMPACT-ENET (CompactLogix Built-in EtherNet/IP Port Fault)?

Ethernet cable disconnected or damaged at the controller RJ45 port. Switch port the controller is connected to has failed or been disabled. Duplicate IP address on the network — controller IP conflicts with another device. Controller Ethernet port hardware failure — rare but possible from ESD or lightning. IGMP snooping misconfigured on managed switch — multicast traffic being blocked

How do I fix fault code AB-COMPACT-ENET?

Check controller Ethernet port link LED — should be GREEN or AMBER indicating link at 100Mbps or 1Gbps. Try a different Ethernet cable — use a known-good patch cable. Ping the controller from engineering laptop — verify basic IP connectivity. Check for IP conflict using Rockwell BOOTP/DHCP server or 'arp -a' on laptop. If using managed switch, check port configuration — ensure port is not disabled or in wrong VLAN. Check controller web page (browse to controller IP) for Ethernet diagnostics and error counts. If CompactLogix 5380 with dual ports, try the other port to isolate the issue

CompactLogix Built-in EtherNet/IP Port Fault

AB-COMPACT-ENET

CompactLogix 5380 or 5480 controller built-in Ethernet port has lost link or detected a fault. Affects I/O connections, HMI, and any device communicating through this port.

high allen-bradley plc

allen-bradley compactlogix 5380 ethernet/ip port network link

Probable Causes (ranked)

Ethernet cable disconnected or damaged at the controller RJ45 port
Switch port the controller is connected to has failed or been disabled
Duplicate IP address on the network — controller IP conflicts with another device
Controller Ethernet port hardware failure — rare but possible from ESD or lightning
IGMP snooping misconfigured on managed switch — multicast traffic being blocked

Fix Steps

1 Check controller Ethernet port link LED — should be GREEN or AMBER indicating link at 100Mbps or 1Gbps
2 Try a different Ethernet cable — use a known-good patch cable
3 Ping the controller from engineering laptop — verify basic IP connectivity
4 Check for IP conflict using Rockwell BOOTP/DHCP server or 'arp -a' on laptop
5 If using managed switch, check port configuration — ensure port is not disabled or in wrong VLAN
6 Check controller web page (browse to controller IP) for Ethernet diagnostics and error counts
7 If CompactLogix 5380 with dual ports, try the other port to isolate the issue

Field Trick

CompactLogix 5380 controllers have two Ethernet ports that can be configured for DLR ring topology. If one port dies, the ring still works through the other. But if you're using both ports for separate networks (not DLR), losing one port means losing one network entirely. Know your topology before troubleshooting.

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