getting complete exception info w/ JDBC (IDS 9.4)

The descriptions for many of the SQLException error codes (ref: http://www-306.ibm.com/software/data/informix/pubs/library/ids_94.html) say "check the accompanying ISAM error code for more information". I would have thought that this additional information would be available via getNextException(). However, this method returns null in at least some cases (eg for "-245 Could not position within a file via an index"). Does anyone know of a programmatic way of fetching the related ISAM code and description?