From DeveloperWorks, Handling unmodeled faults within WebSphere Process Server V6.1
See how BPEL processes can handle unmodeled faults with a user-defined fault handler by using SCA mediation module (ESB) capabilities.
In this article, they talk about handling a scenario where a WSDL SOAP/HTTP service does not define any faults but actually lands up throwing one (StockNoExist). Now, what I would normally do is just edit the WSDL definition used by the BPEL to include the fault definition. This technically works even though the source and target wsdls are different (the fault definition). If you want (or can’t) touch the wsdl then you have to follow the steps in this article to make catching the specific error possible.