On Board Diagnostics

To combat its smog problem in the LA basin, the State of California started requiring emission control systems on 1966 model cars. In California, this entire process is called Smog Control affectionately. The federal government extended these controls nationwide in 1968. Subsequently, our congress passed the Clean Air Act in 1970 and established the Environmental Protection Agency (EPA). This watchdog agency started a series of graduated emission standards and requirements for maintenance of vehicles for extended periods of time. These standards were passed on to manufacturers to produce vehicles that met the standards in hopes of cleaning up the environment. To meet these standards, manufacturers turned to electronically (computer) controlled fuel supply and ignition systems (also A/C). Various sensors measured engine performance and adjusted the supply and combustion systems to provide minimum pollution. The information these sensors provided was the source to provide early diagnostic assistance. The original diagnostics were termed OBD (On Board Diagnostics) and were originally planned to provide information for service technicians to use in the repair of the vehicle. The intentions were good but the planning left much to be desired.

Initially, there were few standards and each manufacturer had their own systems and signals; all tried to set the standard but quickly the term TANS came into being. In early 1988, the Society of Automotive Engineers (SAE) set a standard connector plug and set of diagnostic test signals. The EPA adapted most of their standards from the SAE on board diagnostic programs and recommendations. After seeing what a very short sighted set of guidelines that they had originally adopted, OBD II is a very expanded set of standards and practices, proposed and developed again by SAE and adopted by the EPA and CARB (California Air Resources Board) for implementation by January 1, 1996. Some manufacturers saw the light and actually conformed and produced vehicles under that guideline as early as 1992, much before the mandatory date. They were typically higher end vehicles and the added cost was just absorbed and passed on to the consumer. All manufacturers did the same thing in 1996. Here are some ideas of OBD II:

OBD II - On Board Diagnostic systems are in most cars and light trucks on the road today. During the '70s and early 1980's manufacturers started using electronic means to control engine functions and diagnose engine problems; actually in the '60s for California sold vehicles. This was all primarily conceived and implemented to meet EPA emission standards. Through the years on board diagnostic systems have become more sophisticated and generally more standard in detail, information and interface. OBD II, an upgraded standard announced and introduced in the early '90s, made mandatory in the 1996 vehicles, provides better (than previous systems) engine control and also monitors parts of the chassis, body and accessory devices, giving technicians reasonable information to troubleshoot issues. Information captured also doubles as the diagnostic control network of the car.

The EPA was given the job of reducing "mobile emissions" from cars and trucks and provided with the enforcement power to require manufacturers to make vehicles which meet more stringent emissions standards as they are set. The manufacturers must also provide resources to hold and maintain the emission standards of the cars for the useful life of the vehicle; what the useful life of the vehicle is actually, is the gray area of the industry. OBD II provides a generally common and universal inspection and diagnosis method to verify that the vehicle is performing to OEM standards. While there is much room for debate as to the exact standards and actual methodology employed, the indisputable fact is that there is a foundational need to reduce vehicle emitted pollution levels in all of our cities, certainly the larger ones, and we as citizens and vehicle drivers must conform to these requirements. California leads the battle.

All cars (as opposed to vehicles in general) built since January 1, 1996 have OBD II systems. Some early OBD II (some pre-1996 and some in 1996) vehicles were not 100% compliant due to interpretation of the standard. For who knows what reason, (remember TANS), there are three different interface protocols for OBD II in use, each with minor variations on the communication pattern between the on board diagnostic computer and the various types of scanner consoles or diagnostic tools. There have been some manufacturer changes between protocols in the past few years, seeing advantages or weaknesses of one protocol over another. Though not a hard and fast rule, most Chrysler products, most European and most Asian imports use ISO 9141 circuitry. Most GM manufactured cars and light trucks use the SAE J1850 VPW (Variable Pulse Width Modulation) standard, and most Ford manufactured vehicles use SAE J1850 PWM (Pulse Width Modulation) communication patterns. You can determine which protocol is used on a specific automobile by examining the vehicle's connector socket carefully. If the dash interface connector has a pin in the #7 position and no live pin at socket position #2 or #10, then the vehicle has the ISO 9141 protocol. If no live pin is present in the socket's #7 position, the car uses an SAE protocol. If there are active pins in positions #7 and #2 and/or #10, the vehicle probably uses (though not always) the ISO protocol.

Although there are three different OBD II electrical interface connection protocols, the command set is fixed (the same) according to the SAE J1979 standard. Most OBD vehicles, as opposed to OBD II vehicles, had interface connectors either under the dashboard or under the hood, or both; there was no common location. All OBD II cars have a connector located somewhere in the passenger compartment, supposedly accessible with ease from the driver's seat. Check under the dash, near the fuse block, behind or near the dash ashtray. A cable is plugged into the OBD II J1962 connector and connected to any compatible scan tool. Scanners and other interface tools available range from simple hand held meters that display trouble codes, connections to standard PC computers with special software, up to a large specialty computer with hardware and software used only for such diagnostics.

OBD II signals are most often sought in response to a "CHECK ENGINE" light or "SERVICE ENGINE SOON" light appearing on the dashboard. (In the automotive repair industry, technicians call those lights on your dash a "MIL" or Malfunction Indicator Light. What is wrong with my vehicle?) Sometimes they are sought by a need to resolve engine or control problems experienced with the vehicle. The feedback data provided by OBD II monitoring system can from time to time pinpoint the specific component that has malfunctioned, saving substantial time and cost compared to trial and error repairs; sometimes the information is not specific but at least points the technician to the neighborhood of the problem. Checking OBD II signals can also provide invaluable data for determining the history and the condition of a previously owned vehicle purchase. Gathering, interpreting and possibly resetting the information is sometimes time consuming in itself. MILs show three different generalaties of signals. Occasional flashes show momentary, slice of time malfunctions. The MIL stays on if the problem is of a more serious and continually determinable nature, affecting the emissions output or safety of the vehicle. A perpetually flashing MIL is an indicator of a major problem which can and probably will cause serious damage if the engine is not stopped immediately. In all cases a "slice of time frame" of all sensor readings at the time is recorded in the central computer of the vehicle. Definite failure signals caused by such serious problems will cause the MIL to stay whenever the vehicle is running, and until the problem is repaired and the MIL reset manually or by the computer after a pre-determined number of cycles. Intermittent and temporary failures cause the MIL to light momentarily and they often go out before the problem is located and recorded. The slice of time frame of the vehicle's condition captured in the computer at the time of the malfunction can be invaluable in troubleshooting and diagnosing these troublesome intermittent problems. However, in some cases if the car completes a pre-determined (generally three) driving cycles without a re-occurrence of the problem, the slice of time frame will be erased, termed as being computer reset as opposed to manually reset.

If controlling what happens in an engine and automatic transmission were not sufficient automotive challenges in themselves, a greater one has emerged from OBD II laws, one that cannot be handled any other way that with a very powerful computer. In the case of the automotive industry, most of the companies are using units produced by Intel, the same company that makes the CPUs for most business and personal computers. In this case, the CPU is actually an entire "computer on a chip" with a single job, that of watching a controlling your vehicle's well being. These units are correctly termed microcontrollers but are often called in the automotive industry the CPU, controller, monitor or just computer. As I have described, these OBD laws, specifically OBD II laws, require the constant monitoring of all automotive systems that affect emissions into the environment. Not only does your vehicle's engine control unit have to "watch" what goes on and record troubles for service technicians as they happen, then determine if they are really valid or momentary "glitches", OBD II rules require the prediction of deterioration of the most critical components such as catalytic converter, fuel delivery and evaporative emissions systems, crankshaft and camshaft position sensors, oxygen sensors, manifold air temperature sensor, ignition system and a handful of others, some to be determined in the future.