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Core issue

The %C4K_SWITCHMANAGER-4-S2WERRORREPORT: PimEthAutoNeg: S2w Read/Write Error for port [char] error message is displayed on Cisco Catalyst 4000/4500 Series Switches with 802.3af Power-over-Ethernet (PoE) line cards, and PoE functionality is affected.

This means a read/write error occurred on the specified port.

Sometimes, when using 802.3af PoE cards on Catalyst 4000/4500 Series Switches, phones never get PoE and the connected links never come up. When you disable the PoE functionality by configuring power inline never on a PoE, the interface can still link up when connected to non-PoE devices.

This is a list of the affected 802.3af PoE cards:

  • WS-X4248-RJ45V
  • WS-X4248-RJ21V
  • WS-X4548-GB-RJ45V
  • WS-X4224-RJ45V
  • WS-X4524-RJ45V

These are the observed symptoms:

  • The error message appears on the console.
  • IP phones that receive power from the connected Ethernet ports of the switch lose power.

For more information, refer to Cisco bug ID CSCef87815.


If there is no adverse effect on the functionality of the PoE line cards, treat this message as an informational message only. In this case, no action is required.

As a workaround, try to reseat the affected line card first.  If the error still persists, then please contact Cisco Technical Support online using the TAC Service Request Tool.

Device connected to switch


Cisco IP Phone

Error message


Marius Ilie

Executing the below usually solves the issue:


hw-module module [module no.] reset




@Marius, Thank you for the command/solution. It resolved my problem today.

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