If an ISDU error occurs the OPC UA Service Response array diagnosticInfos[] shall contain at least one element of DataType DiagnosticInfo.

The following rules apply to fill the fields of the DiagnosticInfo structure. The DiagnosticInfo structure does not contain the Strings itself (except additionalInfo), but an index of the position of the String in the stringTable.

Table 70 – Mapping of ISDU Errors in DiagnosticInfo

DiagnosticInfo structure element

ISDU Error related description



IO-Link ErrorType Namespace



Error Code and Additional Code as 4-digit hex number



Locale of localizedText



String that describes the symbolicId

"Subindex not available"


Vendor-specific diagnostic information


The field namespaceUri contains the IO-Link ErrorType Namespace: "http://opcfoundation.org/UA/IOLink/".

The field symbolicId contains the IO-Link Error Code and Additional Code (as described in the IO-Link Specification) as 4-digit hex number converted to a String.

The field locale contains the country and region description of the language that is used in localizedText.

The field localizedText contains a verbal description of the error codes (symbolicId).

Note: This is a String, but not the built-in OPC UA DataType LocalizedText! The content of localizedText is specified in 14.4.

The content of additionalInfo is specified in 14.4.