The sensors to ecm communication is performed on a 5volt reference signal...all the way back to the first CR control system that cummins/bosch/motorola/etc released for these engines. CAN_BUS and/or SCI comm. is only how the vehicle communicates with the engine, 03-05 instrument clusters operate off SCI comm. and 06+ operate off CAN-BUS. The piggybacked ecm will only steal sensor output to convert data to SCI comm. so the 2004 IC can display it.