OBDonUDS - SAE J1979-2

The revision of the diagnostic protocol became necessary because no more unique identifiers were available in several places due to length restrictions, e.g. for DTCs (trouble codes). Especially for the fault memory, data structures have been extended to allow more details on individual faults to be read (e.g. extended snapshot data). In addition, it is now possible to read out for each monitor how often it was actually executed in real driving operation (redesigned IUMPRs = In-Use Monitor Performance Ratio. Parameters for checking diagnostic frequency). In general, it is now possible to read out more and more qualified information on emission-relevant components.

UDS is an established and field-proven standard for manufacturer-specific diagnostics. AUTOSAR software components and many different tools are available for this purpose. Therefore, UDS is an excellent starting point for vehicle diagnostics required by legislation - the standard only needs to be extended to include OBD-specific use cases. The key advantage is thus that there is now only one protocol for diagnostics, rather than two or different ones. Consequently, statutory OBD diagnostics is easier to combine with manufacturer-specific diagnostics, which in turn leads to a significant simplification of ECU software.

At first glance, the previous OBD protocol resembled the UDS protocol, but in detail, the two protocols have many as well as major differences. In practice, the differences resulted in ECUs containing two independent protocol implementations, one for the OBD protocol and another for the UDS protocol. With OBDonUDS, this is no longer necessary. However, new software is required in ECUs to implement OBDonUDS.

In addition, a specification tool is needed to precisely specify the OBDonUDS content for an ECU, which is now even more closely interlinked with manufacturer-specific diagnostics. A new test tool is required to test and validate the OBD portion of the ECU software. The old scan tools no longer work, and new tools are needed here as well. Tool changes are also expected in relation to documentation and archiving.