The J1939 protocol is built upon the CAN (Controller Area Network) bus physical layer. The standard is divided into several parts:
J1939-73 does not define how data is transmitted electrically, but rather what diagnostic messages are transmitted and how they are formatted. Its primary goal is to ensure that a diagnostic tool (commonly known as a Scan Tool) can communicate with any J1939-compliant ECU, regardless of the manufacturer.
Similar to DM1 but restricted to emissions-critical faults (OBD equivalent for heavy-duty). Sae J1939-73 Pdf
Imagine your data logger captures a CAN frame with PGN 65226 (DM1) and byte values indicating:
You open your SAE J1939-73 PDF and search for "SPN 91". You find: The J1939 protocol is built upon the CAN
Without the PDF, troubleshooting would be guesswork.
Yes, but extended. The latest revisions add DM33 for HV battery isolation monitoring and DM34 for traction motor diagnostics. Always download the most recent PDF for EV/HEV work. J1939-73 does not define how data is transmitted
Captures engine conditions (RPM, coolant temp, throttle position) at the moment a DTC was triggered.