I attended an MCI webinar last week on the new engines. Although it won't affect most of us here, 2016/17 engines are falling under a more stringent EPA spec and as a result, Cummins will have an additional 30 new codes to suppliment the ones already existing. The engine computer is going to be testing the quality of the DEF and goodness knows what else. They didn't tell us this, but I wonder how many of the new codes will cause a de-rate or shutdown.
I hate to say it, but I think the days of using an intercity coach as a bus conversion may be coming to an end as the older equipment falls to the wayside. All the newer equipment we have (especially if it uses DEF) needs a much deeper pocketbook to keep running than what most of us are using today.
I think you are referring to HD-OBD. Every manufacturer is going to use the same "codes". Actually, it will be SPN/FMI.
There's nothing wrong with DEF.
This is why I'm using my truck with Caterpillar mechanical 3406B. Caterpillar still makes the 3406C mechanical that is almost identical for use in 3rd world countries for pumps and generators for those that still want a dirt reliable mechanical engine.
Currently, any older RV is exempt from smog laws (at least in California). If it gets to the point of them starting to enforce smog laws on older RV's, I'll have my engine changed to a current Cummins ISL with Allison 3000TRV with 450hp and 1200lb/ft torque. Good Luck, TomC