OBDII decoder diagnostic test mode vehicle diagnostic system OBD technology analysis

1. What is automobile OBD

①OBD (On-Board DiagnosTIc System) is an "on-board diagnostic system". It is a diagnostic system that can warn the driver when a system or related component related to the control system fails. The application of the OBD system is derived from the Euro III emission standard, and the correct function is very important for the control of vehicle emissions. The OBD device monitors multiple systems and components, including the engine, catalytic converter, particulate filter, oxygen sensor, emission control system, fuel system, GER, etc.

OBD is connected to the electronic control unit (ECU) through various emission-related component information. The ECU has the function of detecting and analyzing emission-related faults. When an emission fault occurs, the ECU records the fault information and related codes, and issues a warning through the fault light to inform the driver. The ECU ensures access to and processing of fault information through a standard data interface.

②OBD technology originated in the United States in the 1980s. The early OBD technology used appropriate technical methods to remind drivers of failures or faults. The European Union and Japan introduced OBD technology after 2000. After 2004, OBD technology in developed automobile countries entered the third stage.
There are certain differences between Europe and the United States in terms of OBD detection items and limits. The purpose of OBD monitoring in the United States is to detect faults before becoming a high-emission standard vehicle; the purpose of OBD monitoring in Europe is to detect high-emission vehicles. The OBD technology introduced in China will be equivalent to the relevant regulations of the European OBD system after three stages.
The Euro III emission standard is not equal to OBD. After the mandatory policy of installing OBD was implemented in Beijing on December 1, the vehicle will be Euro III+OBD standard.

③OBD is connected to the electronic control unit (ECU) through various emission-related component information. The ECU has the function of detecting and analyzing emission-related faults. As a result, today's OBD is not only the function of detecting and analyzing emission-related faults, but has extended more powerful functions, heralding the birth of a new industry.

2. The principle of automobile OBD

According to national requirements, starting from July 1, 2007, all new models produced by automobile manufacturers must comply with the National III standard, otherwise they will not be allowed to be sold. That is to say, starting from July 1, 2007, the National III standard will be enforced nationwide, and the National III standard requires the installation of OBD. OBD monitors the engine, catalytic converter, particulate filter, oxygen sensor, emission control system, fuel system, EGR and other systems and components in real time. Then, through the information of different emission-related components, it is connected to the ECU [electronic control unit, which can detect and analyze emission-related faults]. When an emission fault occurs, the ECU records the fault information and related codes, and issues a warning through the fault light to inform the driver. The ECU ensures access to and processing of fault information through a standard data interface.

3. OBD application layer

Application 1:

OBD application functions: fault diagnosis system, oil quantity statistics system, tire pressure monitoring system, safety warning system, acceleration test system, green driving report function, maintenance system, vehicle anti-theft system, value-added system.

Application 2:
★ Application field: enterprise car management, 4S shop, car repair station, car maintenance, car insurance, transportation and other industries .
The role of OBDⅡ

After the implementation of the OBDⅡ plan, any technician can use the same diagnostic instrument to diagnose any car produced according to the standard. One of the mature functions of OBDⅡ is that when the system lights up the fault light, it records the data of all sensors and drivers, which can meet the needs of diagnosis and maintenance to the greatest extent. In the face of increasingly stringent automobile emission regulations in various countries, the goal of OBDⅡ to monitor the efficiency of the emission control system is: as the efficiency of the car decreases during operation, according to the federal test steps, when the car emission level has reached 1.5 times the new car emission standard, the fault light is lit and the fault code is stored. In addition, OBDⅡ also requires the configuration of some additional sensor hardware, such as an additional heated oxygen sensor, which is installed downstream of the catalytic converter exhaust. More precise crankshaft or camshaft position sensors are used to more accurately detect misfires, and all models are equipped with a new 16-pin diagnostic interface. In this way, the computer's capabilities are greatly improved, not only to track component damage, but also to meet the strict limits on vehicle emissions. Scanning tool

OBD Ⅱ regulations stipulate fault codes, a large number of engine management sensor signals, computer commands, etc., which can be read out through a universal scanning tool. Scanning tools can provide a lot of important maintenance information, but many maintenance personnel do not use all of their functions and only use them to read fault codes. In fact, most of the data provided by the scanning tool can be used to find out where the fault is. A particularly effective troubleshooting method is to use a scanning tool and a four-gas (HC, CO, oxygen and carbon dioxide) or five-gas (plus NOx) infrared exhaust gas analyzer at the same time. In this way, the sensor signal or computer command information can be compared with the actual tailpipe exhaust to see if the logical results of these readings are reasonable. Problems caused by the introduction of OBD The introduction of OBD is closely related to four main aspects: usage environment, fuel characteristics, driving habits, and vehicle conditions. Shortcomings in any of these links will affect the expansion and application of OBD. The introduction of OBD technology requires the following related supporting conditions to be improved accordingly: fuel quality, vehicle maintenance skills, consistency of related parts, improvement of driver level, improvement of OBD technology itself, and support from all aspects of society. In a certain period of time, my country's OBD technology is a process of introduction, adaptation, digestion and absorption. Because OBD technology is not only related to the car itself, but also to other links such as fuel and drivers, the introduction and expansion of OBD technology is a test and improvement of the automotive industry chain. Detailed explanation of OBD content of vehicle diagnostic system: