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How Does an OBD2 Reader Works?

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How Does an OBD2 Reader Works?

OBD-II reader

OBD is an abbreviation for On-Board Diagnostics or on-board diagnostics. The term refers to all onboard hardware diagnostic capabilities in most vehicles with an engine and products since the beginning of this century, even if electronic elements are introduced in vehicles since the 80s.

The diagnosis describes the means used to control the components of the vehicle’s micro propulsion group, that is to say, all the elements which participate in its motricity. As for OBD2, it has been gradually implemented since the mid-1990s. It is the standard interface for accessing on-board diagnostic systems.

This interface is mainly used to read DTCs (Diagnostic Trouble Codes). It also provides real-time information from sensors connected to the vehicle’s computers. When a problem has been reported and repair has taken place, the DTCs recorded by the on-board sensors are cleared. With standardized warning lights, the vehicle driver is informed of engine malfunctions. The risk of exceeding the thresholds is signaled by the illumination of the MIL light.


With the OBD2 reader, you can read and clear OBD2 fault codes. It offers a lot of data that provides a reliable idea about the condition of your vehicle in real-time. It is equipped with analysis tools that also allow you to obtain suggested fixes for any type of code error.

There are also auto diagnostic tools with which you can print performance and diagnostic data on your PC. Some brands also offer various functions, such as displaying performance graphs which help you to properly analyze the condition of your engine.

As OBD2 readers are more and more sophisticated, it becomes possible, with a minimum of knowledge, to establish a diagnosis alone for the most apparent faults. They help locate the source of failures and prevent breakdowns. Readers also have the immense advantage of pointing out the excessive amounts of exhaust gases being released from the engine. The warning light will then come on to invite you to check the engine.

Even without having extensive mechanical knowledge, it is easy to understand how the OBD2 reader works. To get there easily, you have to learn to decipher the codes in order to correctly interpret the signals sent.

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The OBD2 reader operates from a diagnostic socket (DLC). Most of the time, it is located under the left side of the dashboard. It should be easily seen near the steering column. It has 16 pins and its shape is triangular. If your vehicle is configured differently, the vehicle owner’s manual should tell you. You can also search online.

You can plug in the OBD2 reader by turning the ignition key first without starting the engine. The reader will already start receiving data from the on-board computer. If the screen does not light up, you need to check the installation of the outlet. On older car models, the sockets are sometimes less effective. In most cases, the OBD2 is connected to the same system as the cigarette lighter.


To start OBD2, you must provide certain data. Often, you need to enter the vehicle registration number as well as the manufacturer’s name and model. Sometimes you also have to enter the type of engine.

Once the device has started, you will be able to find a menu. By selecting “codes”, you will open the main menu with the list of these. Depending on the selection you make and depending on the models, you will see, among other things, active codes and pending codes.

Active codes identify faults that have not yet been resolved. They are therefore always indicated by the indicator light. However, even if the light goes out, the fault may not be resolved.

As for the pending codes, they relate to situations where the OBD2 monitoring elements have not succeeded in carrying out the exhaust gas check correctly. If the monitoring fails again, then the activation code will be activated.


You will more easily understand the operation of the OBD2 reader by familiarizing yourself with the main codes. By learning the meanings of the letters, you will find your way around them more quickly.

For example, the letter P stands for “ engine brake ”. This letter is related to everything related to the engine, transmission or ignition, among others. The letter B, for its part, translates what affects the bodywork. Seat belts and air bags are part of the data included under this letter. As for the letter C, it relates to the power steering system and brake fluid, among others.


An OBD scanner makes it possible to carry out a car diagnosis at a lower cost. Indeed, an OBD-II code reader costs around 20 dollars. This small on-board diagnostic is now within the reach of an individual. A Bluetooth model can connect to a smartphone or tablet to turn it into an analysis tool.

A simple application allows self-diagnosis as it contains most of the information needed to interpret trouble codes. However, this diagnosis does not resolve any problem detected. Some applications even make it possible to erase error codes and thus avoid having to go to a garage.


Today, code readers and OBD scanners are easily found and are widely available. There are many models that can be purchased in stores or on many sites online. In our article on the best OBD code readers, we explain how to choose the right model.

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If you are not interested in purchasing an OBD scanner for self-diagnosis, you can even borrow one. Some tool rental companies can provide you with higher-quality diagnostic tools for a much lower cost than the purchase.


Before looking for an OBD scanner for self-diagnosis, it is also important to understand the difference between OBD-I and OBD-II. Vehicles produced before 1996 are all grouped into the OBD-I category. Designed before the advent of computerized controls, these diagnostic systems do not have much in common with brands. For an OBD-I model, you need to find a scan tool specifically designed for the make of the vehicle.

OBD-II was introduced in the mid-1990s. It is a standard interface for accessing the on-board diagnostic system. Vehicles produced after 1996 are compatible with this system.

The OBD-II interface allows the reading of standardized Diagnostic Trouble Codes, or DTCs, generated by the on-board computer system, as well as real-time information from the sensors connected to the on-board computers. The standard also provides for the erasure of DTCs recorded by the computers when maintenance has been carried out.

In Europe, E-OBD (or European On-Board Diagnostics) has been mandatory since the early 2000s. Failures that lead to exceeding the E-OBD emission thresholds are detected and indicated by a warning light on the dashboard and stored in the memory of the engine control computer.

The bottom line is that you can use any OBD-II code reader on any vehicle produced after 1996. These vehicles all use a common diagnostic connector and a set of universal trouble codes.


Once you’ve got your hands on the correct OBD code reader, the first step is to locate the OBD-II connector. It is usually located under the dashboard to the left of the steering wheel. If you can’t find it, the vehicle’s owner’s manual should tell you. You can also search online for the location of this outlet.

In most cases, the OBD-II connector is fairly easy to find. It is a rectangular-shaped plug and is white in color. With its sixteen pins configured in two rows of eight, it looks a bit like a Scart socket.


Before putting the ignition key on, you can gently insert a code reader into the vehicle’s OBD-II socket. Once the scanner is properly plugged in, you can insert your ignition key and start the engine.

The OBD code reader is then powered. Depending on the model, it can connect via Bluetooth to a smartphone. In an application such as EOBD-Facile for example, the system asks you to indicate the make and model of the vehicle or other information if necessary.

The OBD code reader is then ready for operation. The advanced model will give the possible fault codes with their meaning. An OBD diagnostic application on a smartphone such as EOBD Facile, Car Scanner, or OBD Auto Doctor thus makes it possible to view fault codes (also called DTCs) with their meaning.

The simplest model will simply provide the fault codes. It is then necessary to look for the meaning of these codes on a site that gives the list of standard or generic fault codes. For example, a generic P0380 / P0670 trouble code likely indicates glow plug malfunction. A P0303 code indicates a misfire.


In addition to reading fault codes, an OBD scanner is an auto accessory that can also offer other functions. One of the most useful is the ability to clear fault codes as well as associated diagnostic data after performing a repair. If the code is displayed after a new diagnosis, the problem has not been resolved.

An OBD scanner also provides access to real-time information from sensors connected to the vehicle’s computers. An interface then makes it possible to read the current values ​​of the vehicle’s sensors. It is then for example possible to see the temperature of the coolant, the intake airflow, the engine speed, the engine temperature, the ignition advance, the quantity of air admitted, etc.


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