OBD - On Board Diagnose

The SAE J1939 protocol is used for the diagnosis of (heavy) motor vehicles and utilises the CAN bus.

J1939 is used to detect faults in complex systems, to forward them to various subsystems, for calibration functions, safety functions and read/write access to certain control-unit-internal memories, among other things. All these functions are defined in the J1939-73 standard for off-road and heavy vehicles.

The standard defines an OBD diagnostic connector used for service tools and specifies the messages required to perform diagnostic services. Diagnostic messages (DM) are used both when repairing a vehicle and during vehicle operation. They enable the exchange of diagnostic information between networked control units. This contributes to the development of an intelligent system that can adjust itself in the event of faults or compensate accordingly on the basis of diagnostic information.