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OBD full name: On Board Diagnostics, translated into Chinese is: automatic on-board diagnosis system "OBD" is "on Board Diagnositics II", namely the on-board diagnosis system for type ii. Diagnostic criteria for the automobile emissions and driving fault, from the beginning of 1996, all new cars sold in the United States where, the diagnosis instrument, the fault code and maintenance procedures must be similar to that in accordance with the provisions of OBD program. With the development of economic globalization and internationalization of the car more and more, as the driving and emission diagnosis basis, OBD system will be more and more widely application and implementation. OBD II program makes the automobile fault diagnosis is simple and uniform, repair personnel without special study a new system of every factory.

The OBD system from the engine operating conditions and monitor whether the automobile exhaust, once exceeded, will immediately issued a warning. When the system is failure, the fault (MIL) check engine (Check Engine) warning lights, at the same time the powertrain control module (PCM) fault information will be stored in memory, through certain procedures fault codes can be read from PCM. According to the indication of fault codes, repair personnel to determine the nature and location of the fault quickly and accurately.
OBD real-time monitoring engine, catalytic converter, a particle system and components of collector, oxygen sensor, emission control system, fuel system, such as EGR. And then through the different emission related components of the information is linked to ECU, [electronic control unit, it can detect and analyze fault features associated with emissions], when the discharge fault, ECU fault record information and related code, and through the fault warning lamp, inform the driver. ECU using the standard data interface, to ensure access and process the fault information.
After OBD II project, a technician can use the same diagnosis instrument to diagnose any car according to standard production. One of the OBD II mature function when the system fault lights lit, record all the sensors and actuators of the data, you can maximize meet the needs of the diagnosis and repair. In the face of the increasingly stringent emission regulations, OBD II monitoring emission control system efficiency goal is: with the lower efficiency in the operation of the vehicle, according to the federal test procedure, when 1.5 times the vehicle emissions have reached the level of emission standards for new vehicles, light fault light and stored fault codes. In addition, OBD also requires some additional configuration of hardware, such as additional heating oxygen sensor, installed in the downstream of the catalytic converter exhaust. The more precise the crankshaft or camshaft position sensor, in order to more accurately detect whether the lack of fire, all models equipped with a new 16 pin diagnostic interface. In this way, the ability of computer is greatly improved, can not only damage the tracking component, but also meet the strict limits on emissions from motor vehicles.
OBD system failure timely repair. An annual inspection is limited to control vehicle emissions. But after the vehicle installed OBD is completely different, it can monitor the vehicle emission levels.
If emissions of non-compliance, OBD will be issued a warning, timely notify the driver to repair. Euro III is the most critical of the use of OBD.
In the fault diagnosis of Shanghai Buick, Guangzhou accord sedan, self diagnosis system can display the standard of OBD fault code, such as "PO125", "PO204", representing the speed signal of engine in 5min did not reach 10 degrees C and 4 injector output driver does not respond properly to the control signal.
SAE J2010 provides a standard fault code 5, first letters, 4 behind is the digital.
The first letter indicates the system set the trouble code. The current distribution of letters 4: "P" stands for power system, "B" stands for "C" on behalf of the body, chassis, the "system u" represent undefined.
The second characters are 0, 1, 2 or 3, are as follows: 0 - SAE (American Society of Automotive Engineers) general fault code: 1 - automobile manufacturers in the expansion of the definition of fault code; 2 or 3 characters with system (P, B, C or U) and different. Power system fault codes (P) 2 or SAE 3 is reserved for future use; body or chassis fault code 2 for manufacturers keep body or chassis fault code 3 retained by SAE.
Third characters represent fault system: 1 - fuel or air metering fault; 2 - fuel or air metering fault; 3 - or engine misfire fault; 4 - auxiliary emission control system fault; 5 - car or idle speed control system fault; 6 - computer or output circuit fault. 7, the transmission control system; 8, the transmission control system.
The last two characters that trigger fault code condition. Different sensors, actuators and the distribution of different sections of the digital circuit, the digital representation of the general section of small faults, namely the general fault code; large numbers of spreading codes, provides more specific information, such as voltage is low or high, slow response, or the signal out of range.
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