The EGR inside the ecm of the CM871 is calculated using an overall FRAC value (measuring from 0.000000 - 1.000000). This value can be monitored inside calterm via paramater [ CBL_EGR_Frac_Cmd ] during a monitoring session. It is derrived mainly by lookup tables, such as the 6 tables representing each cylinder [ C_CBR_EGR_Frac_Alpha0_Table ] - [ C_CBR_EGR_Frac_Chi5_Table ]. The initial value plucked from any given table is based on the current speed (rpm) and fueling rate. From there it goes through some upper/lower limiting filters, gets changed based on exhaust temp, etc. the list is long. The frac command is then sent, along with any derates (combustion changes in this case), to the all mighty combustion manager, where other factors of the engine are sent as well. The combustion manager is actually the application in the ecm that does all the work firing the cylinders, changing fueling and charge pressure rates, etc.I am glad somebody finally figured this stuff out and wrote it up. This is the kind of info we need to help understand all this voodoo. I for one have never seen a succinct summary of how EGR is calculated, how DPF loading and cleaning cycles are calculated, or anything like that.