What causes fault code AB-F021 (DeviceNet Scanner Communication Fault)?

DeviceNet cable damage — trunk or drop cable. Node powered off or in fault. Node address conflict — duplicate MAC IDs. Termination resistor missing on one end of trunk. Bus power supply failure — 24V on network dropped

How do I fix fault code AB-F021?

Check scanner I/O tree — identify which node(s) lost communication. Verify node power and status LEDs. Check DeviceNet cable connections — reseat at problem node. Verify termination resistors on both ends of the trunk line. Check network power supply — must be 24VDC ±5%. Use DeviceNet network health analyzer if available

DeviceNet Scanner Communication Fault

AB-F021

DeviceNet scanner module lost communication with one or more nodes on the DeviceNet network.

high allen-bradley

allen-bradley devicenet communication scanner node

Probable Causes (ranked)

DeviceNet cable damage — trunk or drop cable
Node powered off or in fault
Node address conflict — duplicate MAC IDs
Termination resistor missing on one end of trunk
Bus power supply failure — 24V on network dropped

Fix Steps

1 Check scanner I/O tree — identify which node(s) lost communication
2 Verify node power and status LEDs
3 Check DeviceNet cable connections — reseat at problem node
4 Verify termination resistors on both ends of the trunk line
5 Check network power supply — must be 24VDC ±5%
6 Use DeviceNet network health analyzer if available

Field Trick

DeviceNet problems are almost always wiring. Check for the two 121-ohm termination resistors first — one missing resistor can take down the whole network.

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