A5001 fault code in ABB ACS355 drive
directly from the ACS355 FW manual:
5001 - Drive is not responding - Check panel connection.
This can mean that you have a problem on the interface of the communication panel - drive side. If you have other units, again from ACS355, you can try swapping the panel. If the problem persists even on another drive, you will have to change the panel. If the problem no longer occurs, you will probably have to change the drive because the repair is not convenient.
Hope this help you
Source: ACS355 FW Manual