The low coolant is only a warning light AFAIK. It does not interface to the ECM at least on my old 99 ISC engine.
The ECM codes can be found by googling. ISC Fault Codes List- Cummins ECM
are the one for an ISC. You might have an ISL. As you can see there are many codes.
When I had plugged fuel filters (algae) it did not throw codes, just intermittent check engine light under hard acceleration.