IBM 6151 Maintenance And Service Manual page 126

CFx
I/O Channel Error
This SRA number is generated from an error log entry. An I/O
channel error occurred. This error can be caused by any
adapter installed in the system or the system board.
Run the System Checkout to isolate the failure. If a failure is
not detected, suspect any AT 512 KB Memory Expansion
Options installed.
Run the System Checkout to check any repairs.
D1x
Data Link Problem
This SRA number indicates a communication link problem.
D2x
Modem Problem
Run the checkout for the adapter attached to the failing
modem.
If the checkout ends with the message No trouble was found,
go to the maintenance package for the modem. If you do not
have the service responsibility for the modem, inform the
customer that the modem may need servicing.
3-0020-48 Service Manual