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What is J1939? Everything You Need to Know

If you’re interested in better interpreting heavy-duty commercial vehicle fault codes, then gaining a basic understanding of J1939 is an essential start. To help you get started, BenchForce highlights what J1939 is, its history, and various applications.

What is J1939?

Society of Automotive Engineers (SAE) J1939 is a set of manufacturing standards that define how Electronic Control Units (ECUs) communicate via the controller area network (CAN) bus. The CAN bus is a specialized internal communications network that interconnects components inside a vehicle.

More specifically, the SAE J1939 defines five layers in the seven-layer open systems interconnection (OSI) network model. The open systems interconnection (OSI) model is a conceptual model created by the International Organization for Standardization (ISO) that enables diverse communication systems to communicate using standard protocols. Put simply: The OSI provides a standard universal language that allows different computer systems to communicate with each other.

The OSI network model splits a communication system up into seven stacked layers:

  1. Physical Layer: Manages the transmission and reception of raw unstructured data over a physical medium.
  2. Data Link Layer: Ensures reliable data transmission between directly connected nodes by managing data frames and error correction.
  3. Network Layer: Handles the routing and addressing of data across diverse and interconnected networks.
  4. Transport Layer: Provides reliable data transfer by ensuring packets are error-free and in sequence.
  5. Session Layer: Coordinates communication between applications over a network.
  6. Presentation Layer: Translates data into a format the application layer can understand.
  7. Application Layer: Interfaces directly with end-user applications to facilitate network communication.

As a reminder, the session and presentation layers are not part of the J1939 specification.

READ: What Type of OBD Is In My Car? Plus Other FAQs.

When Did J1939 Become the Standard?

In the late 1980s, commercial vehicle manufacturers started adopting electronic systems to improve data sharing and diagnostics. Early implementations of these systems utilized protocols such as SAE J1587 and J1708.

Within this system, J1708 and J1587 were responsible for the physical and application layers, respectively. These protocols became the industry standard as manufacturers shifted from proprietary connectors to the standard 6-pin Deutsch connector, which dominated from the mid-1990s to the early 2000s.

While the SAE J1587/J1708 system was adequate, manufacturers quickly realized its capabilities were constrained. The J1587 protocol could only handle messages up to 21 bytes and had a transmission speed of just 9.6 Kbps. This limitation prompted manufacturers to seek more robust data transmission solutions as the number of sensors in vehicles increased.

To address these constraints, the SAE adopted Bosch’s newly developed CAN 2.0 system in 1991, which offered enhanced data transmission capabilities. This robust CAN protocol subsequently formed the foundation for the new SAE J1939 standard in 1994.

By the mid-2000s, manufacturers were rapidly transitioning to the SAE J1939 protocol from the older SAE J1587/J1708 system. This shift coincided with the rising popularity of 9-pin Deutsch connectors capable of handling increased sensor data. Today, SAE J1939 has become the industry standard for heavy-duty commercial vehicles.

READ: What is a Bricked ECU?

What Kind of Vehicles is J1939 Used For?

Modern vehicles use ECUs to collect, command, and transmit information about their systems and components. All of this information is communicated through a CAN. From speed and torque to temperature and fault codes, ECUs send a myriad of messages.

To ensure all the components of heavy-duty commercial vehicles work effectively, the SAE developed a protocol framework that allows all the CAN components to work together to control the vehicle’s operation and provide info about the vehicle’s health.

The J1939 protocol is widely used across the globe in various types of vehicles, particularly those for heavy-duty applications. Examples of J1939 applications include, but are not limited to:

  • Bulldozers
  • Buses
  • Combine harvesters
  • Excavators
  • Feller Bunchers
  • Fire Engines
  • Garbage trucks
  • Loggers
  • Military vehicles
  • Mining vehicles
  • Motorhomes
  • Semi-trucks
  • Tractors
  • Workboats

These vehicles use the J1939 protocol to facilitate communication between various systems and components, enhancing diagnostics, control, and monitoring capabilities.

However, it’s not only commercial vehicles that support the J1939 protocol. Many large pickup trucks, such as the Duramax diesel and Cummins 4500, leverage this application.

READ: 4 Reasons People Love Ford’s Power Stroke Diesel Engine

Vehicle Wiring for J1939 Applications

If you’re looking for a way to power up an ECU on the bench, you’ll find the BenchForce™ PowerBlock. PowerBlock is a circuit board solution that simplifies a vehicle's wiring into one simple CNC-machined billet aluminum enclosure. (Can we change this link to the J1939 Starter kit instead, or is the PowerBlock landing page better?)

With additional programming harnesses, the PowerBlock can manage nearly any bench programming task for OBD-II, Ford FEPS, Chrysler SCI for JTEC, and J1939 protocols. Simply connect your laptop's USB or serial programming interface to the PowerBlock’s OBD-II diagnostic connector and select from an expanding range of BenchForce ECU harnesses.