http://omronkft.hu/nostree/pdfs/plc/cqm1h/w226-e1-7.pdf
You cannot tell if it is a I/O bus fault or not. The error can be caused by several things.
Connecting via the programming software is the quickest method to determine what has gone wrong with the PLC.
To help determine what the cause is can you determine any of the following:
- Recent work in the panel?
- Last time the battery was changed?
- Did you notice the error after restoring power to the panel?
- How long ago did this machine run?
- When the machine was running, did you notice any flashing lights on the PLC CPU?
It is important to have a copy of the PLC program. Do you have a copy? Any dismantling or removal of power for extended periods of time may cause you to loose the program from the PLC.
If you are going to disconnect the units to check the bus. Here is some information from the manual above.
Note: The wire harnesses for each module can be removed by clips. If the battery in the unit is not working. You will have approximately 2 hours to do this before loosing the program in the PLC.
Hope this helps