IBM 3270 Maintenance Manual page 141

When the first character of the error code is a 4,
5, 6, 7, 8 or 9, the failure is on a memory
expansion adapter.
128KB Memory-Printer Adapter
DO YOU HAVE THE 128KB
MEMORY-PRINTER ADAPTER
INSTALLED?
YES Go to page 3-200-29
NO
3-200-16 Maintenance Information