SAE J1708

📖 YOUCANIC Automotive Glossary

SAE J1708 is a legacy serial protocol for older heavy-duty vehicles from the late 1980s through early 2000s before J1939 replaced it. J1708 uses RS-485 at 9600 baud with SAE J1587 defining the message format. It provides engine diagnostics from Caterpillar, Cummins, Detroit Diesel, and International engines through 6-pin or 9-pin Deutsch connectors.

While superseded by J1939 on newer vehicles, many older trucks, school buses, and commercial vehicles still use J1708. Fleet operators need J1708/J1587 scanner support for pre-2007 heavy-duty diesels. J1708 diagnostic data includes RPM, coolant temp, oil pressure, boost pressure, and fault codes using MID/PID/SID/FMI format.