Messages relating to Client support are in the range DFHZC3202-DFHZC3249 and are written to the CSCC transient data queue (TDQ).
ECI over TCP/IP error messages are in the range DFHIE0001-DFHIE1213 and are written to the CIEO TDQ.
Both sets of messages are listed in your CICS® on System/390® Messages and Codes manual.