Had some back and forth with @specialskoolie
who has pretty much the same engine. He had access to Cummins Insite and hooked the bus up. Here's his response:
If you head to insight and go to features and parameters, there is a
"PTO/REMOTE PTO" option, you can enable and disable the communication to the ECM. That should read "ENABLE" if the switch is working correctly. We changed this and were able to cancel out the HIGH IDLE switch.
If you go over to the "DATA MONITOR/LOGGER" you can see the "REMOTE PTO SWITCH" option, if it is on or off. Regardless of whether it is enabled over on the parameters, you will see this switch on and off because it’s receiving voltage but this doesn’t show if it is communicating to the ECM.
It totally makes sense that they might disable a "PTO" flag before sending the bus on it's way. Now to find a local shop with Cummins Insite access.