This message is a request sent from a diagnostic tool to an ECU to clear its memory of previously active DTCs. After the root cause of a problem is fixed and verified, DM3 is used to erase the DM2 "history log" for that specific fault. It does not clear active faults; DM11 is used for that purpose.
For fleet managers, mechanics, and OEMs, J1939-73 delivers several benefits:
John, a seasoned truck mechanic, was working on a particularly stubborn Peterbilt 389. The truck's dashboard lit up like a Christmas tree, with multiple warning lights indicating various problems. The truck wouldn't start, and the engine control unit (ECU) displayed a string of cryptic error codes. Frustrated and under pressure to get the truck back on the road, John knew he needed to dive deeper into the SAE J1939-73 standard.
SAE J1939-73 is the backbone of heavy-duty vehicle diagnostics. By standardizing how faults are reported, stored, and cleared, it ensures that a complex ecosystem of ECUs can be maintained efficiently. From a mechanic’s scan tool to a cloud-based fleet monitoring system, the principles of DM1, DTC, SPN, and FMI make modern commercial vehicle repair systematic and reliable. As vehicles become more electrified and autonomous, J1939-73 will continue to evolve – but its core mission remains unchanged: providing clear, actionable diagnostic data from every controller on the network.
This is a request message. A diagnostic tool can send a DM3 command to a specific ECU to clear its stored DM2 history and reset certain diagnostic data. Sae J1939-73 Pdf
Instructs Electronic Control Units (ECUs) to wipe their historical fault logs. Behavior: Sent as a request command from a scan tool. 4. DM4: Freeze Frame Parameters (PGN 65229)
What (e.g., Python, C++, or a specific CAN-to-USB adapter) are you using?
You can acquire the standard by visiting the SAE International J1939-73 Product Page .
Reports previously active DTCs that are currently inactive but stored in the module's memory. This message is a request sent from a
The standard outlines a wide range of diagnostic services, categorized by their intended function. These services dictate how data must be requested and formatted in the CAN frames.
DMs provide the essential utilities for off-board service tools (e.g., a laptop with diagnostic software and a vehicle interface adapter) to interact with the vehicle's electronic systems. This includes reading and clearing fault codes, monitoring live data, performing actuator tests, and flashing new software.
Visual logic flows for complex processes like memory security unlocking and multi-packet data transfers.
Monitoring the status of onboard diagnostic (OBD) tests. For fleet managers, mechanics, and OEMs, J1939-73 delivers
Are you developing , building a diagnostic scan tool , or learning for fleet maintenance ?
J1939-73 communicates diagnostic information through standardized Parameter Group Numbers (PGNs) called . While there are over 50 DMs defined in the full specification, a few are fundamental to everyday diagnostics: DM1: Active Diagnostic Trouble Codes (PGN 65226)
The SAE J1939-73 PDF document provides a comprehensive overview of the protocol's specifications, including:
A 5-bit number describing the type of failure (e.g., voltage too high, data erratic, mechanical failure).