I recall the term "Healthy" was used on some DC&AC drives. There was a wire on the drive terminal block call Healthy. Meaning that all internal circuitry was OK, that's why I mentioned AOIs for diagnostics.
I just don't think that the OP has any idea what the OP is asking for.
There is no generic "PLC_Healthy" bit.
There are hard faults, soft faults, logic errors, hardWARE errors, softWARE errors, and lots of things to monitor them, IF POSSIBLE.