On-Board Diagnostics

What Does On-Board Diagnostics Mean?

On-board diagnostics (OBD) is a special system which is implemented in nearly all engine components. It is actually an electronic system which helps in keeping the emission levels of engines in check by monitoring the performance index of various engine components. It, thus, also helps in the checking for any major fault in a component which can damage the whole engine. Another service that an OBD can perform is that it can take information from its various sensors and control the fuel injectors to give the optimum performance.


Techopedia Explains On-Board Diagnostics

An on-board diagnostics system has many different parts such as the sensors, actuators and an Electronic Control Unit (ECU). All these components work in perfect coordination to sense any kind of damage in the system and monitor emission levels of the various parts of the engine. The ECU is like the brain of the system. It collects the data from the various kinds of sensors, for example, oxygen sensors, and analyzes the data. Based on this analysis, it controls the actuators like fuel injectors to give the best performance.

It also has a malfunction indicator light (commonly known as the “check engine” light) which alerts the user in case of any problem in the engine. Many other types of data can be accessed by the owner by a scan tool, which connects to the Data Link Connector (DLC) port. OBD-I systems, which used different scan tools for different vehicle models, began to be included on vehicles in the late 1980s. This was followed by ODB-II, which is still in use and uses a standard connector (SAE J1962). It became a requirement in all cars and light trucks from 1996.


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Margaret Rouse
Technology Expert

Margaret is an award-winning technical writer and teacher known for her ability to explain complex technical subjects to a non-technical business audience. Over the past twenty years, her IT definitions have been published by Que in an encyclopedia of technology terms and cited in articles by the New York Times, Time Magazine, USA Today, ZDNet, PC Magazine, and Discovery Magazine. She joined Techopedia in 2011. Margaret's idea of a fun day is helping IT and business professionals learn to speak each other’s highly specialized languages.