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OBDonUDS (SAE J1979-2): The New Diagnostic Standard for Modern Vehicles
Januar 15, 2012
Across the global automotive and trucking industries, on-board diagnostics (OBD) play a critical role in ensuring vehicles comply with emissions regulations throughout their entire life cycle. For decades, OBD standards have defined what diagnostic data must be available and how external diagnostic tools commonly called scan tools can access that data. Today, that diagnostic landscape is changing.
With the release of SAE J1979-2, often referred to as OBDonUDS or OBD on UDS, the industry is transitioning to a modern diagnostic framework based on Unified Diagnostic Services (UDS). This shift is expected to gradually replace legacy OBD variants across passenger vehicles, trucks, and other regulated vehicle categories in the coming years.
OBDonUDS is the latest evolution of the OBD diagnostic standard defined by SAE J1979-2. It specifies that OBD diagnostic data must now be accessed using the UDS protocol, rather than legacy OBD-specific diagnostic mechanisms. In practical terms:
UDS itself is standardized under ISO 14229 and has been widely used for manufacturer-specific diagnostics for many years. OBDonUDS extends this proven protocol to cover emissions-related and legislated diagnostic use cases as well.
The revision of the OBD diagnostic protocol was driven by several technical and practical limitations in earlier standards.
Legacy OBD protocols relied on fixed-length identifiers. Over time, this led to a shortage of unique identifiers in key areas, particularly for diagnostic trouble codes (DTCs). The lack of expansion capability limited how precisely faults could be described.
Earlier OBD standards provided only basic fault information. Modern vehicles, however, require more detailed diagnostic insight. OBDonUDS introduces extended data structures, enabling richer fault memory content such as:
OBDonUDS enhances support for In-Use Monitor Performance Ratios (IUMPRs). These redesigned parameters make it possible to determine how often specific diagnostic monitors actually ran during real-world vehicle operation, improving compliance verification and diagnostic transparency.
Overall, OBDonUDS allows significantly more detailed and higher-quality information to be retrieved from emission-relevant components.
The decision to base OBDonUDS on UDS was deliberate and strategic.
UDS is a mature, field-proven diagnostic standard already used across the industry for extended and manufacturer-specific diagnostics. It is supported by:
By building OBD diagnostics on UDS, the industry benefits from one unified diagnostic protocol instead of maintaining separate OBD and UDS implementations.
In short, UDS provides a solid technical foundation for legislated diagnostics without reinventing the wheel.
OBDonUDS follows a layered diagnostic model that cleanly separates responsibilities across the communication stack:
Application └── OBD Diagnostic Services └── UDS Stack └── ISO-TP └── CAN
This architecture ensures robustness, scalability, and compatibility with modern vehicle networks.
Historically, different OBD standards evolved for different vehicle categories and markets, including:
These variations increased complexity for OEMs, suppliers, and tool vendors. OBDonUDS is expected to gradually replace these variants, creating a harmonized diagnostic approach across vehicle types ranging from passenger cars to heavy-duty trucks and construction equipment.
OBDonUDS significantly changes how diagnostics are implemented within ECUs.
Although legacy OBD protocols appeared similar to UDS at a high level, they differed in many critical details. As a result, ECUs often contained:
This duplication increased software size, complexity, and validation effort.
However, ECUs must be updated or newly developed to support OBDonUDS-compliant functionality.
The transition to OBDonUDS also affects the diagnostic toolchain.
These changes are expected, but they also bring long-term simplification and consistency.
For commercial vehicles and fleets, OBDonUDS is more than a standards update it is a foundation for future diagnostics.
Key benefits include:
As adoption increases, OBDonUDS will become a standard expectation rather than an exception in trucking platforms.
OBDonUDS, as defined by SAE J1979-2, represents the next generation of on-board diagnostics. By combining regulatory OBD requirements with the proven UDS protocol, the industry gains a unified, scalable, and future-ready diagnostic solution. As vehicle architectures continue to evolve especially in the trucking and heavy-duty sectors OBDonUDS will play a central role in ensuring compliance, reliability, and long-term maintainability. Organizations that understand and adopt OBDonUDS early will be better positioned for the diagnostic challenges of tomorrow.