OBD II: What it Means to YOU


        When I was a teenager working on cars in my family’s driveway, I was fortunate to be able to understand and work on automobiles that were virtually as simple as they were twenty, thirty and even sixty years earlier. That meant that they could still be tuned and, to a certain extent, diagnosed just by how they sounded. Yet only a few years later the first “on board” computers were finding their way into automobiles.

        To meet the government’s increasingly stringent automobile emission and fuel economy standards, the precision control of computers in vehicles was the only hope. Prior to “microprocessor”-controlled ignition systems vehicles had ignition systems that were controlled by mechanical components that worked together to literally switch spark plugs ‘on’ and ‘off’.  This meant that in much the same way that a household light switch ‘clicks’ an electrical circuit ‘on’ and ‘off’ when we sweep the switch up or down, a similar type switch (called “contact points”) in a vehicle’s ignition system clicked open and shut repeatedly to fire engine spark plugs.  While these earlier ignition systems could operate efficiently, inevitably their ‘mechanical’ components would wear out and become less precise over time.

        Based on what has been long referred to as a “solid-state” device since being invented by Bell Laboratories in 1948, the device we now know as the “transistor” was destined to replace motor vehicle “contact points”.  The reason that the transistor was a natural replacement for contact points was because a transistor is also a ‘switch’, though it has no moving parts.   In fact, the transistor was an easy replacement for the vehicle’s ignition “contact points” as it also promised more precision (faster and more accurate electrical ‘switching’) than contact points and also offered the advantage of no mechanical parts to fatigue.  Consequently automakers began to incorporate “transistorized” ignition into mass production to replace “point-type” ignition systems during the mid-1970s.


        Simultaneously, with the arrival of the “catalytic converter” in 1975 came increased requirements for more precision in engine management systems, including fuel injection and spark control.  The higher levels of precision engine management ensured that the sensitive catalytic converter was not overwhelmed with hydrocarbons (unburned fuel), as the efficiency of the catalytic converter relied on a generally well-tuned engine.  The “catalyst” inside of the catalytic converter is a combination of substances that can convert changes in other chemicals while remaining unchanged themselves.  Since the catalyst material is sensitive to exacting chemistry in the engine’s exhaust gases to enable it to ‘clean up’ the pollutants from the engine’s combustion.  In the case of auto exhaust, this means that the catalytic converter turns harmful “hydrocarbons” and “carbon monoxide” gases into less-harmful substances, such as water vapor and carbon dioxide.


        The job of the century-old carburetor of turning liquid gasoline into a vaporized mist as it mixed with air has been phased out and replaced by computer-controlled fuel “injection” of a pressurized mist, increasing combustibility and helping reduce emissions.

        On the ignition side, the conventional “points and condenser” (essentially the mechanical equivalent of a home light switch) that served as the signal to control electrical “zaps” of the spark plugs have been replaced by a transistorized “switch” called a microprocessor.

        What’s even more important today, however, is the principle of feedback that has evolved in today’s automobile computers. Along with the improvements in computerized “engine management” has been the increased ability of the automobile to monitor itself.


        Vehicle computers use a number of sensors to monitor engine and drivetrain operation. For example, by incorporating a device called an “oxygen sensor” just inside the exhaust pipe beyond the engine, the computer can monitor how efficiently the engine is burning fuel.

        If the oxygen (“02”) sensor signals the computer that the engine’s air/fuel mixture is too “rich” with fuel, the engine management computer will adjust the fuel injectors (also called “actuators”) to spray less fuel (leaner).

        Correspondingly, on the ignition side another sensor example is one that monitors the speed of the engine and signals the computer when the crankshaft slows or accelerates. Using this information, the computer can always conclude the exact and optimum moment to switch the spark plug on and off — timing each zap precisely to ensure the best use of the vaporized fuel/air mixture.


        While the computers have been using feedback information, they have also incorporated abilities to record potential engine/sensor malfunctions. This first-generation of these on-board diagnostic (OBD) systems has become increasing sophisticated since the first systems appeared by the 1970s.

        At the same time, technicians have needed more training to tackle the computer troubleshooting that goes on when something doesn’t work properly. Part of this process has involved using the on-board computer memories to “store” information about engine malfunctions in the form of “codes,” or signals, that can be accessed later by technicians using hand-held diagnostic testers.

        The testers, that literally “talk” to vehicle computers, can often obtain codes and other pertinent data to help technicians pinpoint a trouble — such as a defective sensor (feedback) or actuator (engine management/control device). One of the challenges to technicians has been that different manufacturers use different codes to identify system malfunctions.

        This means that a “code 14” may indicate a malfunctioning oxygen sensor on one vehicle brand and a engine speed sensor trouble on another brand. Hmmm. Maybe it would help if all manufacturers shared some of the same computer language to make things easier — as well as some other “standardized” OBD-related terms and diagnostics.

        Consider it done.  Effective with all vehicles sold in the United States since the 1996 model year, the government has mandated the implementation of “OBD II” on new cars, the second generation (hence the “II” of OBD II) of on-board vehicle and emission-control diagnostics — along with enhanced “self monitoring.”

        OBD II standardization will help technicians service 1996 and later vehicles — but also adds a degree of complexity and new training for the automotive service industry.  And even when the computer spots a potential malfunction, your technician still has to troubleshoot. Even computers make mistakes. Whom do you think will troubleshoot them?

        Remember when you used to be the only one who decided it was time to take your car in for a “tune up?” Now you do it by recommended mileage intervals or if your “check engine” light activates.

        With OBD II it’s no longer only up to you — now you’ve got a computer helping to keep your engine in optimum “tune”!

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