DMs provide the essential utilities for off-board service tools (e.g., a laptop with diagnostic software and a vehicle interface adapter) to interact with the vehicle's electronic systems. This includes reading and clearing fault codes, monitoring live data, performing actuator tests, and flashing new software.
Used by a scan tool to request specific DTC lists from a specific ECU address.
A DM is a Parameter Group Number (PGN) that carries one or more DTCs and related status information. The J1939-73 standard defines numerous DMs, but three are the most fundamental: Sae J1939-73 Pdf
SAE J1939-73, titled "Diagnostics – Application Layer," defines how ECUs on a J1939 network communicate diagnostic information. It covers:
Unlike light-duty vehicles that use alphanumeric OBD-II codes (e.g., P0420), heavy-duty vehicles use a four-part Diagnostic Trouble Code structure defined by J1939-73. A single J1939 DTC contains: DMs provide the essential utilities for off-board service
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In conclusion, SAE J1939-73 is a critical standard in the automotive industry, defining the application layer for the J1939 protocol. The SAE J1939-73 PDF document provides a detailed description of the protocol's application layer, enabling ECUs to exchange data seamlessly. The standard's significance lies in its ability to ensure interoperability, facilitate efficient data exchange, and provide diagnostic capabilities. As the automotive industry continues to evolve, the SAE J1939-73 standard will remain an essential component of vehicle network communication. A DM is a Parameter Group Number (PGN)
While robust, J1939-73 has limitations: it does not define flashing or reprogramming of ECUs (covered in J1939-73’s companion, J1939-71 for parameter assignment). Also, the original CAN at 250 or 500 kbps is becoming bandwidth-constrained for advanced diagnostics with many ECUs. SAE has therefore extended the standard to to support CAN FD (flexible data-rate) for larger payloads.