Automotive Diagnostic Systems: History of OBD

The first two aspects about advanced automotive diagnostic systems (AADS) are 1) the basic principles of automotive fault diagnosis pretty much have remained unchanged over the years. While systems have changed in technology, the notions that systems fail and need diagnosis have not. 2) On Board Diagnostics (OBD) means intelligent diagnosis, and this relies on sensors and computer programming. These automotive diagnostic systems also go under other rubrics, such as “intelligent automotive diagnostics”, “automated automotive diagnosis”, “computerized automotive diagnosis”, and so forth.  A common term is Vehicle Automated Diagnostic System. [1]

Brief history of OBD

First, to place our discussion in context we can refer briefly to some history about the development of automotive diagnostic techniques to appreciate where we are today.  Prior to the 1950s, the “old days”, most discovery of problems in automotive systems was done with just a few gauges and the rest by hand – listening to awkward sounds, smelling strange odors, and otherwise using the senses to detect problems.  As vehicles became more complex, we entered a “Middle ages” in the 1960s, where there was more of a reliance upon instrumentation. Video display terminals could show the electronic characteristics of the electronic system, and as computers became more readily available, other measurements, such as vacuum, oil pressure, and various temperatures could be integrated into a machine-based diagnostic system. 

Like in other fields, in automotive fault diagnosis, humans were increasingly removed from the loop, and computers took over until we are now at the stage of on-board diagnosis (OBD). Sensors are attached to various components, such as a cooling system’s thermostat, and a wire runs from that through a harness and to a terminal block, which, in turn, is plugged into a diagnostic machine outside the car. There also are on board diagnostic indicators, such as warning lights, gauges, and readouts from a computer that tell the driver or technician the vehicle’s condition.  These, as history would have it, stem from the earliest days of on board gauges, such as fuel level indicators, cooling system gauges, oil pressure gauges, and tachometers that record the engine speed. Added to this are oxygen sensors, engine temperature gauges, and any device to measure fuel flow, vacuum, and factor that enters into fuel consumption.

Computerized systems started coming on line in 1969, with Volkswagen’s fuel injected models in Type III, followed by Datsun’s sporty 280Z. In 1980 General Motors implemented its computerized assembly line diagnostic link (ALDL) that read out error codes at the rate of 160 baud.  The ALDL also is known as the assembly line communications link or ALCL.  By 1986, the speed went to 8192 baud with the universal asynchronous receiver/transmitter (UART) at half-duplex, or one way transmission, until we had in the beginning of this millennium complete OBD packages [2].  There were three main types of ALDL arrangements of pins on the connector (also known as “pinout”):

12-pin ALDL connector pinout:
10-pin ALDL connector pinout:
5-pin ALDL connector pinout:
4A B C D E
Table 1: GM used the 12 pin arrangement, Lotus the 10 pin, and others the 5 pin.

The various numbers of pins was only the beginning of the interoperability problem.  From system toi system, each pin had a different function, the signaling protocol was irregular, and, although many pin arrangements had one pin each reserved for power, ground, and data, GM, the leader in the field, did not have the power pin reserved for the battery voltage. 

During the 1994-1995 period, General Motors introduced an intermediate version of OBD-I and OBD-II, which involved a 16 pin connector and measurement of oxygen after exhaust went through a catalytic converter. To indicate the degree of variance among vehicles, we have the following as an example; there are the 94-95 Corvettes with one post-catalyst oxygen sensor (but two catalytic converters), this being only a subset of the OBD-II codes [3]. GM H-body cars in 94-95 had this hybrid system, as well as other styles and models but only in certain years [4]. 

Brief legal history of OBD

Legal requirements for OBD vary throughout the world, of course, but we can point to some leaders in mandating the systems. The European Union, the U.S., Australian, and Chinaare considered. The primary impetus for requiring OBD is maintaining air quality. Two aspects are central: what the OBD does and the standardization. 

In the United States, California has been considered the leader in air quality control standards, and people know the state for its strict requirements for air pollution control equipment on cars. Even back in the 1970s, people were required to have such things as positive crankcase ventilation (PCV) valves and air injection pumps.  If people didn’t have them, they had to install that equipment. Not surprisingly, the California Air Resources Board (CARB) started requiring OBD equipment on all new automobiles in 1991. Often, people refer to this as “OBD-I”, because this was the first major widespread requirement for it, but neither the connector nor the data link protocol were standardized.  Only when equipment and codes were standardized did the OBD-II emerge. Prompted by the smog alerts inLos Angelesand rapidly growing population, CARB in 1994 required that all cars of model year 1996-onward be equipped with OBD-II. The SAE’s recommended connector and protocols were incorporated into the regulation [5]. As might have been expected, the U.S. government required that all new cars sold have OBD-II.   The European Union on 13 October 1998 stated that all cars sold needed to have OBD-II. Specifically, gasoline-powered cars had to have it starting with model year 2001 and diesel vehicles, starting with model year 2003 [6].

Everything was tumbling head over heels, with the various reports coming from the United Nations and scientific organizations about global warming. Even with the reticence of the climate deniers in Washington, the U.S. Congress required in 2008 that all cars sold there incorporate the ISO 15765-4 [2] signaling standard (a variant of the Controller Area Network (CAN) bus).

Consciousness awakening was occurring in China, as a result of its extremely rapid and often uncontrolled growth. Numerous Chinese cities were becoming contaminated to the point one could not see more than a mile distant. Respiratory problems were mounting, and the numerous coal-fired generating plants, along with the enormous degree of air pollution from vehicles caught the attention from even the most bureaucratic and corrupt sectors of government. One could not ignore the increasingly alarming situation. Accordingly, the Environmental Protection Administration Office in 2008 required that certain light vehicles implement OBD (standard GB18352) by July 1, 2008 [7].   However, the regulation allowed for some regional exemptions.

Following the European Union’s lead in 1998, the U.S. Congress, under a somewhat more environmentally enlightened administration mandated in 2010 the heavy duty on-board diagnostics (HDOBD) for some commercial (non-passenger car) engines sold in the United States[8]. In all of these regulations, there is no requirement for a specific technology, only that the OBD-II be implemented and that it incorporate specific standards. 

Advanced Automotive Diagnostic Systems
Don’t miss the “Advanced Automotive Diagnostic Systems” Conference, taking place 27-29 June 2011 at the Dorint Pallas in Wiesbaden, Germany.
[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 -

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Posted on June 8, 2011, in ALL, Electric / Electronic. Bookmark the permalink. 2 Comments.

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