J1939: A Common Language Across Manufacturers

Written by
The MurCal Blogster
Published on
October 28, 2022 at 12:27:49 PM PDT October 28, 2022 at 12:27:49 PM PDTth, October 28, 2022 at 12:27:49 PM PDT

What is it?

J1939 is a set of standards defined by SAE (Society of Automotive Engineers) for networking and communication in the commercial vehicle sector. They are used in heavy-duty vehicles such as trucks and buses, ships to ski lifts, mobile hydraulics, etc. The focal point of the application is the networking of the powertrain.




In the late 1980s, commercial trucks began implementing electronic systems for sharing information and extracting diagnostic data. One of the first electronic systems used was based on protocols SAE J1587 and J1708. The J1708 defined the physical layer of the system, while J1587 defined the application layer and the communication system. 


Unfortunately, while the SAE J1587/J1708 system worked well, the J1587 messages were limited to 21 bytes and transmitted at a speed of only 9.6 Kbps.

Hence the SAE while creating the new CAN 2.0 system in 1991, they increased the transmission, and this protocol served as the base for the new SAE J1939 standard.


SAE J1939 was initially released in 1994, and around the mid-2000s, manufacturers began switching to it. Today, the SAE J1939 500k standard has practically replaced former standards and is expected to continue expanding because of its reliability and functionality.

Basics of J1939


The J1939 is a high-level protocol that runs on top of Controller Area Network (CAN). It uses 29-bit Identifiers in the message headers and Program Group Number (PGN) messages to exchange data, which are automatically transmitted or available upon request. It includes a definition of standard PGN messages and includes a proprietary message range for OEMs to use in their applications and supports diagnostic messages (DM1 Active and DM2 Previous) and larger than 8-byte message transmission using BAMs (Broadcast Announce Messages).

The maximum network trunk length for J1939 is 40 meters and the max drop length is three meters. The standard network transmission rate is 250k bits per second, but some applications support 125k and 500k; it also runs on a standard CAN network so the physical layer requires two 120 ohm resistors (terminators) at each end of the network

Industry Applications

-Diesel Engine Manufacturers

-Oil & gas equipment – frack trucks, pumps, sand kings

-Marine vessels – wheel house to engine

-Locomotives – engine system telemetry

-Commercial, construction, agricultural and recreational vehicles

-Electric power generation (diesel gensets)

-Water and wastewater systems – pumps, valves

-Testing and validation – vehicle and component test systems



J1939 Codes

In total, an SAE J1939 message typically consists of a minimum of 93 bits and tells users the exact source and nature of data, which can be used to diagnose issues as they arise. J1939 messages consist of an identifier and associated parameters. Signals start with 29 bits called the "message" that identify the source, and then continue with 54 bits that contain 8-byte data parameters, or "signals." 


The identifier contains a PGN, while the parameters consist of SPNs.


PGN: A PGN is a unique identifier that comes at the beginning of the J1939 message. It consists of the first three bits indicating the priority, 17 bits for the PGN, and 8 bits for the source address.

SPN: An SPN is a Suspect Parameters Number, which is functionally equivalent to a PID. From 1 to 511, SPN and PID numbers are almost identical, but SPN numbers go beyond 511 to over 50,000. SPNs are grouped after the PGN in a DTC.

The J1939 Connector


In J1939, the connector is a 9-pin Deutsch connector. It's a standardized interface with the J1939 network of most heavy-duty vehicles.


MurCal’s J1939 CAN Bus input/output modules from Trombetta are designed for cost savings, easy installation, and minimization of equipment. All modules are precision-engineered for accuracy, stability, and performance.

J1939 CAN Bus Input/Output Modules | MurCal


Take your integration to the next level with superior control, enhanced diagnostics and increased efficiency with Modules by Enovation Controls. Their CAN I/O and fan control modules are designed to complete any system for total equipment control.

J1939 CAN Bus Input/Output Modules | MurCal


J1939 protocol is the accepted industry standard and the vehicle network of choice for off-highway machines in the mass transportation, construction, agricultural machinery, material handling, forestry, maritime and military industries. It is a higher-layer protocol based on Controller Area Network (CAN), providing serial data communications between microprocessor systems (also called Electronic Control Units - ECU) in any heavy-duty vehicle. These messages include vehicle road speed, torque control message from the transmission to the engine, oil temperature, and many more.

Our team works closely with you to customize your equipment for optimal efficiency using J1939 input/ output modules. 


Contact us for help in determining which module will work best for your machinery.

Phone: 661-272-4700

Email: sales@MurCal.Com

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