Green House Gas (GHG) Phase 2 regulations take effect on EPA MY21 and newer North America On Highway product.  Engine fuel map data under GHG Phase 2 regulations will be an input to most (but not all) vehicle GHG certification.  Changing engine rating changes the fuel map, which in turn might also affect vehicle GHG compliance.  Under GHG Phase 2, EPA can evaluate engine manufacturer compliance based on the fuel map, and OEM compliance based on the vehicle, including the fuel map.  OEMs also manage their own overall vehicle GHG compliance including AB&T (Averaging, Banking & Trading) reporting, etc.  This is relevant because, under GHG Phase 2, it is possible an OEM can retire credits where a change in engine fuel map data puts it over a relevant GHG standard.  No re-rate of an individual MY21 and newer North America On Highway unit shall occur until a formal approval process is in place and the OEM grants the approval for the unit in question through that process.  For full details refer to TSB200206, distributors can refer to PPC 5953.