Fault code provides a machine-readable identifier that can be used to programmatically identify the error condition and respond as appropriate. The SOAP specifications define the following fault codes specific to SOAP 1.1 and 1.2.
SOAP 1.1. VersionMismatch, MustUnderstand, Client, and Server.
SOAP 1.2. VersionMismatch, MustUnderstand, DataEncodingUnknown, Sender, and Receiver.
In addition to those fault codes defined by the SOAP specifications, Windows Communication Foundation (WCF) uses fault codes defined by each Web services specification that it implements.