A JCOM1939 Engineering Note on Error Handling, Bus Off, and Silent Mode in Two-Node CAN Networks JCOM1939.com | Copperhill Technologies | © 2026 Controller Area Network (CAN) is well known for its robustness. Arbitration prevents message collisions from corrupting data, error detection identifies damaged frames, automatic retransmission provides another opportunity…
Posts published in “SAE J1939 Basics”
When engineers troubleshoot a CAN network, they usually focus on the messages flowing across the bus. They check identifiers, decode data bytes, and verify timing. While that is certainly important, there is another source of diagnostic information that is often overlooked—and in many cases, it provides the fastest path to…
If you’ve worked with SAE J1939 long enough, you’ve probably experienced the frustration of connecting two devices to a CAN bus and seeing… absolutely nothing happen. No engine data. No diagnostic messages. No responses to requests. Just silence. The good news is that most J1939 communication problems are caused by…
One question that appears regularly in SAE J1939 discussions is whether multiple Electronic Control Units (ECUs) can transmit the same Parameter Group Number (PGN). At first glance, the answer seems straightforward: if the J1939 standard defines a message, why shouldn’t multiple devices be allowed to transmit it? In reality, the…
One of the more common questions when analyzing or simulating SAE J1939 traffic is surprisingly simple: “How accurate must a J1939 message frequency be?” If a message is supposed to be transmitted every 100 milliseconds, does that mean exactly 100 milliseconds? Can it be 101 milliseconds? 105 milliseconds? What happens…
If you are new to SAE J1939, the first thing you will probably do is search for the official standards documents. That usually leads to an immediate moment of confusion. You discover that SAE J1939 is not a single document. It is an entire collection of standards. Hundreds of pages.…
SAE J1939-22 is the CAN FD evolution of the J1939 family. In SAE’s own high-level description, it brings CAN’s flexible data rate capability into J1939 to support higher efficiency, parallel transactions, functional safety, and cybersecurity-oriented extensions, while preserving the J1939 application model built around PGNs, SPNs, source addresses, requests, diagnostics,…
I have long been a vocal critic of the barely readable standards issued by SAE International. And to be fair, SAE is hardly alone—standards bodies, as a species, seem united by a peculiar compulsion: the need to prove their intellectual worth by rendering their documents as impenetrable as possible. Clarity,…
Have you ever wondered how a heavy-duty truck knows something is wrong—before the driver even notices? Behind that quiet intelligence sits a structured conversation between electronic control units (ECUs), all speaking the same language: SAE J1939. It’s the backbone of communication in modern trucks, buses, construction equipment, and industrial machinery—and…
Modern heavy-duty vehicles and industrial machines rely on robust, real-time communication between electronic control units to operate safely, efficiently, and predictably. For engineers working in automotive, transportation, and industrial environments, understanding how data is exchanged, prioritized, diagnosed, and analyzed across complex vehicle networks is no longer optional—it is essential. CAN…
