SAE J1939-73 is a standard developed by the Society of Automotive Engineers (SAE) that defines the Diagnostics layer of the J1939 communication protocol. While the J1939 family as a whole governs how electronic control units (ECUs) communicate in heavy-duty vehicles, J1939-73 specifically outlines the procedures for identifying and reporting system failures, retrieving diagnostic data, and configuring vehicle parameters. It is the industry standard for diagnostic communication in commercial vehicles, agricultural machinery, and construction equipment.
SAE J1939-73, titled "Diagnostics – Application Layer," defines how ECUs on a J1939 network communicate diagnostic information. It covers: Sae J1939-73 Pdf
Note: The SPN is the evolution of the Parameter Number (PN) defined in J1939-71, specifically reserved for identifying fault sources. Bytes A–C: SPN (low, med, high parts) —