If you spend enough time around CAN Bus and SAE J1939 discussions, you’ll eventually encounter a statement along these lines: “Why implement a J1939 stack in firmware when Linux already supports J1939?” It’s a fair question. Modern Linux kernels include native J1939 support as part of the SocketCAN framework, and…
Posts published in “Misc. J1939”
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 spend enough time around CAN bus systems, you eventually encounter the magical little box known as the CAN repeater. Depending on who is explaining it, the device is either: the cure for all network problems, a way to build “unlimited” CAN networks, a signal booster, or a mysterious…
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.…
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,…
When engineers, telematics providers, and fleet managers discuss SAE J1939 for fleet management, one truth becomes immediately apparent: Not all PGNs are created equal. Modern heavy-duty vehicles broadcast hundreds of parameter groups across the network, but in real-world fleet management applications, only a relatively small subset of PGNs carries the…
Electronic Logging Devices (ELDs) are regulated embedded systems used in commercial vehicles to automatically record Hours of Service (HOS) data in compliance with U.S. FMCSA requirements. From an engineering standpoint, an ELD is a vehicle-connected data acquisition and logging system with strict regulatory, reliability, and tamper-resistance constraints. This report provides…
SAE J1939 defines a comprehensive framework for message formatting, transport, and network behavior in heavy-duty vehicle systems. While many Parameter Group Numbers (PGNs) are publicly standardized, a substantial portion of real-world J1939 traffic consists of proprietary messages. These messages are intentionally undocumented by OEMs and are often central to machine…
Please consider! The DEF Sensor Simulator is not an off-the-shelf device. It was originally created by a team of automotive engineers as a proof-of-concept solution for bypassing malfunctioning DEF sensors. The project consists of a parts list and open-source control code, and anyone using it must assemble and program the…
A recent internal market study by Copperhill Technologies uncovered a surprising but critical shortcoming across all commercially available SAE J1939 baud rate converters: none of them explicitly address the issue of Silent or Listen-Only Mode. This omission, whether in marketing descriptions or technical documentation, can have significant implications for system…
