On-Board Diagnosis System II - Volkswagen Technical Site

Overview of OBD-II (Gasoline Engine)
Basic Concept of OBD-II
Since 1970 the California Air Resources Board History of pollutant emissions
(CARB) has tried everything within its power to in California:
curb atmospheric pollution by imposing statutory
requirements.
The concepts which these efforts have spawned,
such as OBD-I (1985) for example, have already Emission limits
contributed to a welcome reduction in the emission
values of motor vehicles. 100%
80%
60%
40%
20%
0%
HC
CO
NOx
1975 1980 1985 1990 1995 2000
Year
175_002
Malfunctions and faulty components in the
engine management system can lead to a drastic
increase in pollutant emission.
In view of the technical complexity involved, the
concentrations of
CO – carbon dioxide
HC– hydrocarbons, and
NOx – nitrogen oxides
cannot be measured directly. Instead, they are
determined by testing the components of the
engine management system which affect exhaust
emissions.
This also has the advantage that faults can be
traced directly by using a Scan Tool.
175_003
6