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OBD II originated in 1982. At a time when the us California air resources board (ARB) began to establish a regulations, requirements since 1988 all the vehicles sold in California must be equipped with on-board diagnosis system to control emissions system of failure. Early on-board diagnosis system (now called OBD I) is more simple, only monitoring oxygen sensors, an EGR system, fuel supplying system and engine control module.

OBD I in the right direction, but has obvious defects.

A. the lack of uniform standards. Each different manufacturers and different models lack of unified standard between, make after-sales maintenance, the different models must use different plugs. In some systems, still must use expensive special decoder. Therefore, when they started for ARB now obd code reader setting standards. The main content of the standard are as follows:

1) standardized 16 needle diagnosis a (DLC), the specified with the function of the designated needle;

2) standardized electronic agreement;

3) standardized diagnosis code (DTC);

4) standardized technology.

B. monitoring function is not strong. Some problems OBD I can’t monitoring, such as catalytic converters completely failure or have been removed, ignition of fire and fuel evaporation pollution emission problems. Moreover, OBD I only when the failure has been happened to light MIL lamp, it can’t monitor to the parts and emission of the gradual damage.

So, obviously need a more precise more complex system.

Finally worked out the next generation ARB OBD system standard, and has set up a file in 1989 official, called OBD II. The new standards implementation requires a starting period. Until 1996, the car factory in California to the standard vehicle on the new standard is implementation.

The same new standard in 1990 to the federal air cleaning method, it require all 49 states vehicles in 1996 on all equipment OBD II. But there is a small grace, is will strictly abide by laws and regulations as the time in 1999. So, some 1996 years of OBD II system may lack a obd ii scanner standard features, such as fuel evaporation pollution emission clean test.

Although OBD II technology is still relatively new, not the maintenance market after a major impact, but the impact will happen. The system of government regulations to the failure of the emission control systems warned, so, all 1996 car and all the equipment units OBD II. But the first application of obd code reader time is 1994 years.

And before it of OBD II all car since the diagnosis system different place is in the strict targeted. In other words, when the vehicle emissions of HC, CO and NOx or fuel evaporation cleaner than FTP standard 1.5 times of light MIL. This includes random of fire engine when the HC emissions caused by the overall rise; The catalytic converter purification efficiency of down to a certain limit; under System of detecting sealed fuel system has air leakage; An EGR system fault from NOx emissions of rise; A key sensor or other emissions control equipment failure, etc. That is, even in the car seems to the normal operation, without any actual exercise performance problems, MIL lamp light up.

However, equipment of the vehicle OBD II Scanner MIL lamp’s main purpose is to remind drivers, the vehicle emissions of overweight, need to repair.