J1939/73 specifies the diagnostic layer for a J1939 network and is the only application layer published and supported for J1939. This specification is responsible for defining all diagnostic layer SPNs and PGNs. J1939-73 defines messages for active faults, passive faults, and clearing faults. Also messages for OBD-2 compliance and flash bootloader operation (i.e. erase and programing of flash).