OBD2 system

What is?

- OBD is an on-board diagnostic system for vehicles (cars and trucks). Currently OBD2 (United States), EOBD (Europe) and JOBD (Japan) standards are used that provide complete monitoring and control of the engine and other vehicle devices.

History and future

- In the 1950s most of the discovery of problems in automotive systems was done with only a few meters and the rest at hand: listening to engine sounds, smelling strange odors, and otherwise using the senses to detect problems. As vehicles became more complex, entering the 60's, where there was more reliance on instrumentation. Display devices could display electronic features of the electronic system, and as computers became more readily available, other measurements such as vacuum, oil pressure and various temperatures could be integrated into a machine-based diagnostic system.

- The number of sensors increases, connected to different components, and wires runs from these to terminal blocks where a diagnostic machine can be connected. There are also onboard diagnostic indicators such as lights, gauges and readings from a computer (switchboard) that tell the driver the condition of the vehicle.

- These are the first days of on-board fuel level gauges, cooling system gauges, oil pressure gauges, tachometers that record engine speed, oxygen sensors, engine temperature gauges and any device to measure the fuel flow, vacuum and the fuel consumption factor.

- Computerized systems started coming on line in 1969, with Volkswagen’s fuel injected models in Type III, followed by Datsun’s sporty 280Z. In 1980 General Motors implemented its computerized assembly line diagnostic link (ALDL) that read out error codes at the rate of 160 baud. The ALDL also is known as the assembly line communications link or ALCL. By 1986, the speed went to 8192 baud with the universal asynchronous receiver/transmitter (UART) at half-duplex, or one way transmission.

- In the early 1970s, vehicles sold in the United States were equipped with electronics to control various systems and diagnose car faults, with the aim of minimizing pollution. This occurred with the passage of the Clean Air Act and the establishment of the Environmental Protection Agency (EPA) in 1970. This electronics varied between manufacturers and the year of the model.

- California has been considered the leader in air quality control standards, and people know the state for its strict requirements for air pollution control equipment on cars. Even back in the 1970s, people were required to have such things as positive crankcase ventilation (PCV) valves and air injection pumps. If people didn’t have them, they had to install that equipment.

- In 1979 The Society of Automotive Engineers (SAE) recommends a standardized diagnostic connector and set of diagnostic test signals. Not surprisingly, in 1991 the California Air Resources Board (CARB) requires that all new vehicles sold in California in 1991 and newer vehicles have some basic OBD capability. These requirements are generally referred to as "OBD-I", though this name is not applied until the introduction of OBD-II. The data link connector and its position are not standardized, nor is the data protocol. In order for the driver to detect a malfunction indicated by the OBD, the obligation to have a lamp indicating the MIL (Malfunction Indicator Lamp) was imposed. They only monitored some of the emissions-related components, and were not calibrated for a specific level of emissions.

- Prompted by the smog alerts in Los Angeles and rapidly growing population, CARB in 1994 required that all cars of model year 1996-onward be equipped with OBD-II. The SAE’s recommended connector and protocols were incorporated into the regulation. As might have been expected, the U.S. government required that all new cars sold needed to have OBD-II.

- The European Union on 13 October 1998, according to the Directive 98 / 69EG, stated that all cars sold needed to have OBD-II. Specifically, gasoline cars had to have it starting with model year 2000 and diesel vehicles starting with model year 2003. Likewise also trucks from 2005 onwards must be provided with an OBD.

- U.S. Congress required in 2008 that all cars sold there incorporate the ISO 15765-4 [2] signaling standard (a variant of the Controller Area Network (CAN) bus).

- The next planned stage is OBD-III, in which the cars themselves communicate with the authorities if there is a worsening of harmful gas emissions while on the road. If this happens you will be asked, through an indicative card, to correct the defects.


- OBD-II is the second generation of the on-board diagnostic system, OBD-I successor. It alerts the driver when the emissions level is 1.5 higher than those designed. Unlike OBD I, OBD-II detects electrical, chemical and mechanical failures that can affect the vehicle's emissions level. For example, with OBD I, the driver would not notice a chemical failure of the catalyst. With OBD-II, the two oxygen sensors, one before and the other after the catalyst, ensure good chemical status.

- The system checks the status of all sensors involved in emissions, such as injection or air inlet to the engine. When something goes wrong, the system automatically notifies the driver by turning on the Malfunction Indication Lamp (MIL), also known as a Check Engine or Service Engine Soon.

- To provide the maximum possible information for the mechanic, it keeps a record of the fault and the conditions in which it occurred. Each fault has an assigned code. The mechanic can read the logs with a device that sends commands to the OBD-II system called PID (Parameter ID).

- Usually the OBD-II connector is located in the driver's feet, center console, or under the passenger's seat.

- At the moment, it is possible to connect to the diagnostics machine in different ways, via Bluetooth, WiFi, USB, dropping the connection protocol via the serial port (RS232). This link, coupled with software running from a computer or a mobile terminal, allows real-time monitoring of error codes and various parameters directly from the engine control unit such as engine revolutions, fuel consumption in real time or the oil temperature, among many other parameters depending on the model. The ELM327 controller is the most extended to establish such links between the motor control unit and the device with the software installed.


- EOBD is the abbreviation for European On Board Diagnostics, the European variation of OBD-II. One of the differences is that evaporations from the fuel tank are not monitored. However, EOBD is a much more sophisticated system than OBD-II as it uses "maps" of inputs to sensors based on the operating conditions of the motor, and the components adapt to the system by calibrating themselves empirically. This means that parts need to be high quality and specific to the vehicle and model. More information on this link.


- JOBD is a version of OBD-II for vehicles sold in Japan.

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