The SAE J1708 specification was defined by the SAE and TMC in 1986. Its main purpose is to address the transmission of electronic signals and information among truck and bus components (i.e. Electronic Control Units or ECUs).

J1708 is mainly used on heavy-duty and commercial vehicles. It defines the physical layer and data link layer. Common application and transport layers used on J1708 are J1587 and J1922. J1587 communicates diagnostic information, while J1922 communicates control data. J1708 is outdated and is currently being phased out of production. It is being replaced by J1939.

J1708 Data Link

J1708 is a differential serial communications bus which is half duplex and multi-master (i.e. multi-drop). It uses 8, N, 1 byte framing and has a network speed of 9600 bits per second (bps). The first byte of every message is the MID, which stands for message identifier. Every message ends with a twos complement checksum.