This article is part of our comprehensive SAE J1939 online documentation.
The Society of Automotive Engineers (SAE) Truck and Bus Control and Communications Subcommittee has developed a comprehensive set of standards governing the design and implementation of devices that transmit electronic signals and control information among vehicle components. SAE J1939, along with its companion documents, has rapidly become the industry standard and the preferred Controller Area Network (CAN) protocol for off-highway machinery used in construction, material handling, and forestry applications.
SAE J1939 is a higher-layer protocol built on the CAN bus, facilitating serial data communication between microprocessor-based systems, also known as Electronic Control Units (ECUs), in heavy-duty vehicles. These ECUs exchange critical operational data, including vehicle speed, torque control messages between the transmission and engine, oil temperature, and a wide range of other performance metrics essential for vehicle functionality and efficiency.
The key advantages of using CAN as a field-bus technology include reduced wiring—requiring only two wires between nodes—highly reliable communication, ease of implementation, and enhanced maintenance and service capabilities. These benefits not only improve vehicle performance but also contribute to lower production costs, making CAN an efficient and cost-effective solution for modern vehicle networks.
J1939-based protocols are used in:
- Diesel power-train applications
- In-Vehicle networks for trucks and buses
- Agriculture and forestry machinery (ISO 11783)
- Truck-Trailer connections
- Military vehicles (MiLCAN)
- Fleet management systems
- Recreational vehicles
- Marine navigation systems (NMEA2000)
The protocol features of J1939 are derived from two earlier SAE (Society of Automotive Engineers) specifications:
1. SAE J1708
SAE J1708 defines the physical layer of the communication link, utilizing RS485 as its electrical layer with a transmission rate of 9600 baud. Unlike RS232/485, CAN prevents message collisions, ensuring more reliable communication. In J1708, messages begin with a Message Identification Character, followed by the data payload and a checksum. Each message has a maximum length of 21 characters, with each data character consisting of 10 bits. Transmission starts with a start bit of low polarity.
2. SAE J1587
SAE J1587, a joint effort between SAE and TMS, establishes “Recommended Practices for Electronic Data Exchange Between Microcomputer Systems in Heavy-Duty Vehicle Applications.” It standardizes communication and data exchange between ECUs operating over J1708 networks, ensuring compatibility and structured messaging.
J1939 was developed to replicate and enhance the functionality of J1708 and J1587 while incorporating support for control systems. Depending on application requirements, vehicles may implement either or both specifications.
The J1939 standard is extensively documented in the SAE J1939 Standards Collection, which provides comprehensive guidelines for its implementation and use.
| Document | Description |
| J1939 | Recommended Practice for a Serial Control and Communications Vehicle Network[1] |
| J1939/01 | Recommended Practice for Control And Communications Network for On-Highway Equipment |
| J1939/02 | Agricultural and Forestry Off-Road Machinery Control and Communication Network[2] |
| J1939/11 | Physical Layer – 250k bits/s, Twisted Shielded Pair |
| J1939/13 | Off-Board Diagnostics Connector |
| J1939/15 | Reduced Physical Layer, 250k bits/sec, Un-Shielded Twisted Pair (UTP) |
| J1939/21 | Data Link Layer |
| J1939/31 | Network Layer |
| J1939/71 | Vehicle Application Layer |
| J1939/73 | Application Layer – Diagnostics |
| J1939/74 | Application – Configurable Messaging |
| J1939/75 | Application Layer – Generator Sets and Industrial |
| J1939/81 | Network Management |
[1] This document does exist, however, the hyperlink on the SAE web site produces an error message.
[2] This document is not listed in the “Core J1939 Standards” list on the SAE web site, but it can be found through their search feature. Reference: http://www.sae.org/technical/standards/J1939/2_200608
SAE J1939 is an intelligently designed protocol that efficiently leverages the CAN 29-bit message identifier. Instead of relying on a complex array of protocol functions, J1939 utilizes predefined parameter tables, ensuring the protocol remains structured and easy to understand. It exemplifies the principles of practical and effective engineering, following the KISS (Keep It Simple, Stupid!) philosophy, while still being as powerful and efficient as any other higher-layer protocol built on CAN.
Unlike other CAN-based protocols, J1939 does not follow the conventional Master/Slave or Client/Server architecture. Instead, it embraces the Multi-Master approach, where the node that wins the bus arbitration acts as the master while all other nodes function as slaves. This design choice simplifies network communication while maintaining robust and efficient data exchange.
SAE J1939 Starter Kit and Network Simulator
Our JCOM.J1939 Starter Kit and Network Simulator is designed to allow the experienced engineer and the beginner to experiment with SAE J1939 data communication without the need to connect to a real-world J1939 network, i.e., a diesel engine. It may sound obvious, but you need at least two nodes to establish a network. That fact applies especially to CAN/J1939, where the CAN controller shuts down after transmitting data without receiving a response. Therefore, our jCOM.J1939 Starter Kit and Network Simulator consists of two J1939 nodes, namely our jCOM.J1939.USB, an SAE J1939 ECU Simulator Board with USB Port.
The jCOM.J1939.USB gateway board is a high-performance, low-latency vehicle network adapter for SAE J1939 applications. The board supports the full SAE J1939 protocol according to J1939/81 Network Management (Address Claiming) and J1939/21 Transport Protocol (TP).
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