AUTOSAR Diagnostic Communication Manager Specification for software implementation details.
SAE J1939-73 is the "language" of heavy-duty vehicle repair. By standardizing how faults are reported and how data is accessed, it ensures that a single diagnostic tool can communicate effectively with engines, transmissions, and braking systems from various manufacturers. Sae J1939-73 Pdf
No. Passenger car OBD-II uses ISO 15765 or SAE J1979. Heavy-duty OBD is based on J1939-73 but adds extra emission-specific DMs (DM12, DM23). However, many heavy-duty scan tools provide both. Sae J1939-73 Pdf
J1939-73 defines the "Diagnostic Messages" (DMs) that act as the vehicle's internal reporting system: Sae J1939-73 Pdf