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SAE J1939/84

On-road engine emission test specification

SAE International, the society of automotive engineers, has published an updated version of the J1939/84 Recommended Practice. The document specifies a set of test related to emissions of heavy-duty, on-road vehicles.

The SAE J1939/84 open-source implementation is available on Sourceforge (Photo: Controltec)

THE RECOMMENDED PRACTICE IS TITLED “OBD Communications Compliance Test Cases for Heavy Duty Components and Vehicles”. It comprises guidelines for communicating in accordance with the diagnostic messages specified in SAE J1939/73, with the use of an off-board diagnostic tool interface.

Mark Zachos, chair of SAE International’s J1939/84 Task Force under the Truck Bus Control and Communications Network Committee, said the Recommended Practice was created to assure that heavy-duty engine manufacturers are complying with standardized emission testing regulations. Zachos said the specification assures that all engines, regardless of the manufacturer, can be tested under the same set of tests to determine if they meet governmental emission regulations. “Engines designs differ from manufacturer to manufacturer, so we needed to create a Recommended Practice that could apply to all engines,” Zachos said. “This is what SAE International does best. We were able to create a Recommended Practice that works on all fronts.”

SAE J1939/84 describes the tests, methods and results for verifying diagnostic communications from an off-board diagnostic tool, such as a scanner, to a vehicle or component. The Recommended Practice serves as a guide for testing vehicles for compliance with California Air Resources Board and other requirements for emissions-related, on-board diagnostic functions for heavy duty engines used in medium and heavy duty vehicles. The development of heavy-duty, on-board diagnostic regulations by the U.S. EPA and the California Air Resources Board require that diagnostic message services are exercised to evaluate diagnostic communication standardization requirements on production vehicles.

“This updated version of SAE J1939/84 revises the testing procedures in section six of the older version of the document in order to implement a two-operating cycle failure detection process for production vehicle evaluation,” said Zachos. “The tests also exercise diagnostic executive features, such as three-drive cycle accounting, freeze frame management and the general demeanor in addition to the demonstration of interface functions. Detailed criteria for some tests are described in a normative appendix, Appendix A, which was inserted before the output report examples that are now in Appendix B. The revisions were extensive enough to warrant publication as a complete revision.”

Sourceforge has started an open-source project implementing the SAE J1939/84 test specification. A first version has been released three month ago. Controltec is one of the sponsors, who has partnered with the heavy-duty vehicle industry to provide an open-source implementation of SAE J1939/84. Sourceforge is a web-based service that offers a source code repository, downloads mirrors, bug tracking and other features. It is a location that software developers can use to control and manage free or open-source software developments.

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