Q1/2025 J1939 and vehicle controls blog

This blog by Bryan Hennessy will provide updates on the wider topics under discussion within the J1939 committees. Bryan is an experienced engineer in the fields of CAN diagnostics, marine electronics and semiconductors. He is an active member of the SAE Truck and Bus Control and Communications Network Committee and J1939 Task Force and chairs the ‘J1939-21 – Data Link Layer Task Force’.

The Truck and Bus Control and Communications Network Committee (TBCCNC, or SAE J1939 standards committee) met virtually for four days of standards development and maintenance meetings between 17th February and 20th February 2025. Here is a summary of the directions being taken by the committee and the task forces working under it. This group meets every quarter in these structured and productive engineering meetings, and anyone who wants to get involved can join as a guest. 

The meetings started with a thorough update from the Truck Trailer Interface Task Force. This task force is working with other standards bodies to significantly increase communications between the front end of the rig, or the tracker, and the towed vehicles, or the trailers. They are about 60% of the way to developing the first SAE standard to update this communications link, which still uses SAE J560. The standard dates from 1974 and has been updated many times. The new standard will carry camera data, full controls, wireless communications, active suspension, and much more. It will use two Ethernet and two CAN channels, gateways, and will have a cloud connection. This is an exciting standard to follow because of the many possibilities and improvements it brings to anyone who drives on the roads or uses goods that are delivered by truck. i.e. all of us! 

Next was the J1939-21/22 Datalink Layer document update and maintenance meetings. We’re going into intense levels of detail during this meeting, but comments were made during this meeting that got the task force chairman thinking about a way to update the structure of some documents that have been “teaching engineers an incorrect OSI layer model for years”. If anything comes from these ideas, it will be reported to the industry then. 

CARB (California Air Resource Board) came into the conversation during the On-Board Data (OBD) discussion that followed. Changes are still being made to storage rules around fault codes, what’s stored and for how long, particulate matter, and NOx monitoring, all related to diesel engines. A good portion of this meeting was also spent discussing issues related to CO2 Family Certification Level (FCL), the emission standard for the engine family. As we continue to increase monitoring of CO2 emissions and continue to see an increase in electric power trains, mostly for CO2 reduction, I expect to see more monitoring rules related to this primary greenhouse gas. 

A task force that has been on hold for a few years was reinstated this quarter, the J1939 DC Charging Interface Task Force. This task force is standardizing the controls between the EV (Electric Vehicle) and the megawatt EVSE (Electric Vehicle Service Equipment), or put simply, ‘the big EV charger’. CAN will be one of the two communications protocols between these two pieces of equipment, and the CAN messages that control this interface are being standardized with J1939 formats under SAE, ISO, and IEC as I type this. The SAE standard that will govern these chargers is J3271, and it, along with the other standards mentioned, covers everything needed to understand either end of this big charger connection. The SAE J3271 standard is expected to be released later this year at a Recommended Practice (RP) level and will enable an industry that is waiting to move forward a well-documented path to do so. 

Cybersecurity is a growing concern in many industries, including trucking, and this is why there are three documents under J1939 that are being developed to address it. 

• SAE J1939-91A – Security Recommendations for Interfaces to On-Vehicle Networks 
• SAE J1939-91B – Security Recommendations for Wireless Interfaces 
• SAE J1939-91C – CAN FD Network Security 

The Cybersecurity meeting was one of the best attended meetings this week, showing that this topic has strong interest in the commercial transportation industry. Much of the meeting was spent talking about how to use the provisions built into the J1939-22 CAN FD specification to carry J1939-91C security data. 

Next, we worked on J1939-31 Network Layer issues. The specific issue that dominated this meeting is seen when a Network Interface ECU is used to interface a J1939-21 (CAN CC) network and a J1939-22 (CAN FD) network. When translating between these two frame formats, and using Transport Protocol (TP) and FD transport, meeting all the timing requirements gets complicated. The task force chairman presented some useful technical slides to provide insight into the issues involved. Other factors that were considered are Cut-Through vs. Store-Forward methods, RTS/CTS vs. BAM transfers, and the number of packets to be sent per RTS/CTS. After much discussion some complicated conclusions were arrived at, and it was agreed that this subject should remain open for further consideration. 

For the NextGen Task Force we received an excellent presentation from Softing Automotive about the software defined vehicle and ADAS history and future. 

During the meeting of the J1939 Digital Annex Task Force, there were many new Manufacturer IDs requested from both the agriculture and NMEA (marine) industries. This indicates significant activity in those industries with many new companies wanting to put devices on a J1939 network. There were also thirty-three engineers in the Digital Annex meeting, which is a larger number than usual. 

• SAE J1939 Introduction
• SAE J1939 DBC files now available for use by CAN software
• MathWorks and Kvaser Present: Using J1939 logged field data for Data Analysis and Model-Based Design
• ATI and Kvaser J1939 and CANLab Webinar
• In-Vehicle Communication Standards for Trucks: Where Do We Go With J1939?
• Bryan Hennessy’s Q1/2024 SAE J3271 update