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What is OBD-II System?

Posted by AINOPE Official on

What is OBD System?

OBD stands for On-Board Diagnostic. It is a computer-based system to monitor the performance of the vehicle and control emissions. When there is something wrong with the system, the MIL(Malfunction Indicator Light), also known as “Check Engine” light will be on, and the OBD system will store the trouble information to read the concerned trouble codes through standard diagnostic instrument and Diagnostic Connector. With the globalization of the economy and the increasing internationalization of automobiles, OBDⅡsystem, as a basis for driving and emission diagnostics, will be more widely implemented and applied. And it will make vehicle diagnostic easy and unified, there is no need for maintenance personnel to master new system of different manufacturers .

Features of OBDⅡsystem:

1. The OBD connector has positions for 16 pins.

2. With DATA LINK CONNECTOR (DLC) function.

3. Unify the same fault codes in different vehicles and its meaning.

4. With dash camera function.

5. With function to re-display the memory trouble codes.

6. With function to clear the fault codes directly by the diagnostic instrument.


Error code:

SAE J2010 stipulated a five-digit standard fault codes. It begins with a letter, follows four-digit number. The first letter indicates the system in which the fault code is set. At present, there are four letters are available. “P” indicates power system, “B” indicates body, “C” indicates chassis, “U” indicates undefined system.
The second character is 0,1,2 or 3. Below is the meaning of each of them;

0---SAE, universal trouble codes defined by Society of Automotive Engineers 1---spread trouble codes defined by auto manufactures.

2 or 3---vary from system letter P, B,C or U. Number 2 or 3 in power system is reserved by SAE for future use. Number 2 in body or chassis trouble codes is reserved by manufacture, number 3 in body or chassis trouble codes is reserved by SAE.


The third character indicates the malfunction system:

1--- fuel & air metering

2---fuel & air metering

3---ignition failure or engine misfire

4---auxiliary emission control system failure

5---vehicle or idle speed control system failure

6---computer or output circuit failure

7---transmission control system failure

8---transmission control system failure


The last two characters indicate the cause of the trouble codes. Different sensors, actuators, and circuits are assigned numbers in different segments. The smaller number in the segment indicates a general fault, that is, the general fault code; the larger number indicates the spread code, providing more specific information, such as low voltage. Or high, slow response, or signal out of range.

The OBD interface is usually placed above the accelerator pedal or under the dashboard. More specific vehicle installation locations can be found by consulting a car consultant or using the OBD+ car model. All cars are required to install an OBD system before leaving the factory.

Attention: The alarm will ring only when the emissions are not up to standard. However, it will be invalid to install OBD if the oil is unqualified. Almost all cars produced after 2005 can use OBD Ⅱ system.


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