SYSTEM COMPLETION CODE=EC6 REASON CODE=0000FD1D can be found in z/OS SYSTEM CODES:
Explanation: An error occurred during processing of a callable service to z/OS UNIX System Services (z/OS UNIX). The callable service may have been originally issued as a function in a program or as a shell command.
Depending on the source of the abnormal end, register 15 may or may not contain a hexadecimal reason code.
The reason codes are in the form xxxx yyyy, where xxxx represents internal information (not described here) and yyyy represents external information shown below.
The Reason code in this case was 0000FD1D
An additional message in the JES messages for the abended CV job describes the meaning of this particular Reason Code (which can also be found in the same z/OS SYSTEM CODES manual):
TERMINATED BY SIGNAL SIGXCPU, DUE TO CPU TIME OUT.
What we found in this case is that prior to the upgrade client specified TIME=NOLIMIT on the EXEC card in the CV startup JCL, but after the upgrade this TIME parameter was omitted.
Once they added it back, the SEC6 Reason 0000FD1D no longer occurred.