Applicable Systems
MicroLogix
CompactLogix
ControlLogix
PowerFlex
Symptoms
The controller has lost communication on the EtherNet/IP network. The module status LED flashes red and connected devices show a connection timeout.
Possible Causes
- Ethernet cable damaged or connector loose at the controller port
- IP address conflict on the network causing intermittent connectivity
- Network switch power loss or port failure
- Controller network module firmware corrupted after a power surge
Troubleshooting Steps
- Step 1: Check the Ethernet cable connection at both ends and inspect for damage
Replace the cable if visibly damaged; verify with a cable tester - Step 2: Verify the controller IP address is unique on the network
Use the ARP command from a laptop to check for duplicate addresses - Step 3: Verify the network switch has power and the port LED is active
Move the cable to a known-good port if the port LED is dark - Step 4: If the network module firmware is suspect, reflash from the programming software
Use the latest firmware from the manufacturer's website
How to Reset
Reset: Communication restores automatically once the link is re-established. Clear the fault in the controller diagnostic buffer.
Common Replacement Parts
- Ethernet cable: Cat 5e, industrial shielded (Use RJ45 or M12 connectors per environment)
- Network switch: 5-port unmanaged, industrial (Verify PoE requirements)
Frequently Asked Questions
- Q: How do I find a duplicate IP?
Disconnect the controller and ping its IP from a laptop. If the ping succeeds, another device is using the same address.
- Q: What is EtherNet/IP?
An industrial protocol using standard Ethernet for real-time control. CIP (Common Industrial Protocol) provides the application layer.
- Q: Can I use a managed switch?
Yes, managed switches provide VLAN, QoS, and diagnostics for larger networks. Configure QoS to prioritize CIP traffic.
Source: OEM Technical Manual
Category: PLC & VFD