Automotive Diagnostic Systems: From OBD to Open Diagnostics Exchange format (ODX)

Limits and potentials of standardization processes

Before getting to ODX, itself, we need a quick review of OBD. Electronic ignitions and fuel injection systems were the first major steps in getting away from mechanical fuel delivery and ignition. Being able to control the volume of fuel and sparking it at the right time are critical in controlling emissions, as well as making the vehicle more fuel efficient. Miniaturization and developments in computer technology enabled a closer control over that efficiency, and, along with it, the monitoring of contaminants. 

All the while the technology was unfolding it was realized that not only that it was beneficial but that it needed standardization. The diagnostic codes needed to be read in a manner better than specialized machines. A brief word is needed about standardization processes. They do not often occur in a convivial environment, as there are many competing commercial interests. Many times, a corporation will invest millions of dollars in developing a product, hoping that others will follow suit. There is a catch, however, if people can become dependent upon the way that product acts, then, the developers stand potentially to gain enormously from patent rights. A classic case of dependency was with the fiber optic FC (“ferrule connector”). During the early 1990s, there were many fights in the Electronic Industries Association and Institute for Electrical and Electronics Engineers standards committees among fiber optic cable developers about which standard was to prevail. It would be more convenient for everyone to follow, but more important, if everyone had to use company X’s product because it was the standard, then that dependency would be established. The same is true for automotive diagnostic equipment being standardized. Major corporations will send representatives to these standardization committees to thrash out the issues and present their arguments. While not the usual decorum, physical fights have been known to break out at these standardization meetings.

In 1988 the Society of Automotive Engineers argued for a uniform diagnostic connector and standardized test signals. After it became apparent that the original OBD was not going to be very useful for universal use or for governments to incorporate into air quality legislation pertaining to automobiles, it was realized that further work was needed. Hence, came the OBD-II development.

Yet, there are still exist many problems in standardization. For example, automobile manufacturers use five basic OBD-II protocols:

  • J1850 PWM
  • J1850 VPW
  • ISO9141
  • ISO14230 (also known as Keyword Protocol 2000)
  • CAN (ISO15765/SAEJ2480)

Chrysler, as well as every European manufacturer and the majority of the Asian manufacturers use ISO 9141 circuitry. GM uses SAE variable pulse width modulation (VPM) patterns, while Ford uses SAE J1850 pulse width modulation (PWM) patterns. These three communicate with the standard 16-pin, J1962 connector, but there are different protocols. One can differentiate between the pin usage by inspection. Systems using the ISO 9141 protocol locate a pin in position number 7 and a pin in either position number 2 or 10 position. SAE protocol-based systems do not have pins with connections in position number 7.

There are systems called ‘OBD-II‘ that are compliant with laws and goes by the name of “European OBD (EOBD). There also is the Japanese variety, called ‘JOBD’ [10]. 

Specifically standard to the OBD-II are:

      • Type of connectors and number of pins – 16
      • Signaling protocols that can be used – limited to the five
      • Format of messages
      • A list of what is to be monitored
      • Methods for data coding
      • Power pin that can connect to the car battery
      • List of diagnostic trouble codes (DTC)

Based on all this ODX  was able to be created.  As indicated by its name, Open Diagnostics Exchange format”, or ODX, the industry was moving towards a uniform way of OBD. The Association for Standardization of Automation and Measuring Systems [12] is responsible for the ODX. ASAM was initiated by German car manufacturers and, in its own words, “…provides standards for data models, interfaces and syntax specifications for a variety of applications, such as testing, evaluation and simulation.”  Actually, ODX is a “market name”, the actual name being “Data Model for ECU [electronic control unit] Diagnostics (also: Open Diagnostic Data Exchange Format) V2.2.0 18 May 2008 [13].” Since 1998, numerous automobile manufacturers from all around the world have joined, and jointly, they create standardsfor International Organization for Standards (ISO) approval [14].   The ODX, created in 2002, went numerous revisions, and is stable enough for use. There were 25 core members, 19 companies, and three countries that formed the standard [A report by the ODX ISO project leader, A. Schleicher is available on-line [15]. As specified by the ISO website:

The ODX specification contains the data model to describe all diagnostic data of a vehicle and physical ECU, e.g. diagnostic trouble codes, data parameters, identification data, input/output parameters, ECU configuration (variant coding) data and communication parameters. ODX is described in Unified Modelling Language (UML) diagrams and the data exchange format uses Extensible Mark-up Language (XML).

The ODX modelled diagnostic data describe:

  • protocol specification for diagnostic communication of ECUs;
  • communication parameters for different protocols and data link layers and for ECU software;
  • ECU programming data (Flash);
  • related vehicle interface description (connectors and pinout);
  • functional description of diagnostic capabilities of a network of ECUs;
  • ECU configuration data (variant coding).

The purpose of ISO 22901-1:2008 is to ensure that diagnostic data from any vehicle manufacturer is independent of the testing hardware and protocol software supplied by any test equipment manufacturer.

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[1]  VAD –
[3]  – 1994 Corvette Service Manual, Book 2. General Motors Corporation. December 1993. pp. 6E3–A-166: 6E3–A-223.
[5] CCR Title 13 Section 1968.1 and 40 CFR Part 86 Section 86.094
[6] European emission standards Directive 98/69/EC
[12] ASAM –
Further Reading – OBD not yet required for heavy duty vehicles.
In the U.S.various states have requirements,Californiabeing the traditional leader, here.  

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Posted on June 3, 2011, in ALL, Electric / Electronic. Bookmark the permalink. 1 Comment.

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