Introduction to OBD

As early as the early 1980s, many automakers in the developed countries of the automotive industry began to use EFI engines extensively. The first generation of onboard diagnostics system is provided in the EFI engine control system. Afterwards, the onboard fault diagnosis system is gradually applied in the microcomputer-controlled automatic transmission, anti-lock braking system, airbag and cruise system. . The system can monitor the working conditions of various parts of the system at any time during the working process of the electronic control device. When the electronic control system fails, the fault information is stored in the microcomputer, and the vehicle maintenance personnel crosses the corresponding in the diagnostic connector according to the prescribed method. Terminals, analyze and diagnose the faults of the vehicle's electronic control system.

History of OBD development

The concept of OBD was first introduced by General Motors (GM) in 1982 with the aim of monitoring emissions control systems. Once a fault is detected, the OBD system will light an indicator on the dashboard to inform the driver and record a code in the onboard computer (commonly referred to as the engine control unit or module, ie ECU or ECM). Device acquisition for easy troubleshooting. GM proposed this concept to the attention of the California Air Resources Board (CARB). CARB adopted the standards set by SAE in 1985, requiring all vehicles sold in California from MY 1988 to have some basic OBD functions. Later, the US Environmental Protection Agency (EPA) required that all new cars sold in the United States must meet the relevant OBD technical requirements since 1991, which is what was later called OBD-I.

The Society of Automotive Engineers (SAE) further standardized the technical details of diagnostic interfaces and communication methods. On this basis, OBD-I developed into the second generation OBD, namely OBD-II.

OBD-II has made great progress in diagnostic functions and standardization. The fault indicator, diagnostic connection, communication protocol between the external device and the ECU, and the fault code are all specified by the corresponding standards. In addition, OBD-II can provide more data to be read by external devices. These data include fault codes, real-time data for some important signals or indicators, and frozen information. Since then, on October 13, 1998, the European Union commissioned the ISO organization to establish the EOBD standard in OBD-II. China also formulated a set of COBD standards on the EOBD standard on April 5, 2005.

The new generation of wireless transmission system OBDIII system can use the small car wireless transceiver system to automatically notify the management department of the vehicle's VIN, fault code and location by wireless cellular communication, satellite communication or GPS system. The management department issues instructions on the level of the vehicle's emissions problem, including recommendations for where to go for repairs, and the time limit for solving emissions problems. This information can be punished on vehicles based on improper regulations that cause excessive emissions.

 History of OBD2 development

What is the difference between the American standard and the European standard?

3.1 Diagnostic seat joint definition is different

The diagnostic connector structure of the on-board fault diagnosis system in the United States and Europe is the same. Both use a unified 16-terminal diagnostic connector, but the terminal definitions are slightly different. Terminals 1, 3, 4, 5, 8, 9, 11 The definitions of 12, 13, and 16 are the same, in which the terminal 4 is the chassis grounding, the terminal 5 is the signal grounding, the terminal 16 is connected to the battery positive pole, and the others are reserved for use by the manufacturer. US OBD-II uses terminals 2, 6, 10, and 14 as data transmission terminals, and terminals 2 and 10 are SAE J1850 communication data transmission terminals. If the CAN bus technology is used in the automotive electronic control system, the terminals 6, 14 are defined as CAN data transmission terminals, which are respectively connected to the two signal lines CAN High and CAN Low of the CAN bus. If the CAN bus is used at the end, the terminals 6, 14 are reserved for use by the manufacturer. Terminals 7, 15 are reserved for use by the manufacturer.

European OBD-II uses terminals 7, 15 as ISO 9141-2 or ISO/DIS 14230 communication data transmission terminals. According to the requirements of the communication protocol, the electronic control unit (ECU) communicates with the test instrument through the diagnostic connector, and can communicate with a single line (K line) or with two lines (K line and L line). When using single-wire communication, terminal 7 and K line are connected, terminal 15 is reserved for use by the manufacturer, and when using two-wire communication, terminal 7 and K line are connected, and terminal 15 and L line are connected. Terminals 2, 6, 10, 14 are reserved for use by the manufacturer.

3.2 different communication protocol definitions

The OBD-II standard uses three communication protocols: SAE J1850 PWM (Pulse Width Modulation), SAE J1850 VPM (Variable Pulse Width Modulation), ISO 9141-2 (or ISO/DIS 14230-4), and other communication pin definitions. To be determined. Typically, European cars use the ISO 9141-2 communication protocol, and other communication pin definitions are pending.

 Specific classification of automotive network standards

Since 1980, many internationally renowned automobile companies have been actively engaged in the research and application of automotive network technology. The use of the automotive network solves the problems caused by the point-to-point body wiring, making the body wiring more standardized and standardized, reducing the cost and enhancing the stability. So far, there are various network standards such as Bosch's CAN, SAE's J1850, ISO's VAN, Philips' D2B, and LIN's LIN. To facilitate research and design use, the Society of Automotive Engineers (SAE) classifies automotive networks into categories A, B, and C based on speed.