The standard is divided into several parts, each serving a distinct function:
| Standard | Layer | What it Does | | :--- | :--- | :--- | | J1939-11 | Physical | Defines the 250kbps twisted shielded pair | | J1939-21 | Data Link | Defines CAN frames, PGNs, and transport protocol | | | Application (Diagnostic) | Meaning of diagnostic data | | J1939-71 | Application (Vehicle) | Defines non-diagnostic parameters (speed, fuel rate) | | J1939-84 | OBD | Defines on-board diagnostics for emissions | Sae J1939-73 Pdf
: Detail the most critical messages defined by the standard: DM1 (Active DTCs) The standard is divided into several parts, each
J1939-73/1 is a companion document specifically for Off-Board Diagnostics (test equipment connected via a diagnostic tool). The main J1939-73 covers both in-vehicle (on-board) and some off-board messaging. To fully appreciate the content of the J1939-73
of the J1939 protocol stack, which is the communication standard for heavy-duty vehicles like trucks and buses.
To fully appreciate the content of the J1939-73 PDF, you must master three core concepts: SPNs, FMIs, and DM messages.