Volkswagen said on Monday that 11 million of its diesel cars worldwide were equipped with software that was used to cheat on emissions tests.

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How Did the System Work?

The software sensed when the car was being tested and then activated equipment that reduced emissions, United States officials said. But the software turned the equipment off during regular driving, increasing emissions far above legal limits, possibly to save fuel or to improve the car’s torque and acceleration.
It is not yet known which systems were modified. But experts are focusing on parts of the exhaust system that are designed to reduce emissions of nitrogen oxide, a pollutant that can cause emphysema, bronchitis and other respiratory diseases.


Exhaust system of a Volkswagen Golf

Volkswagen has used two basic types of technology to reduce emissions of nitrogen oxides from diesel engines, by either trapping the pollutants or treating them with urea. The first type is shown here.

Nitrogen oxide trap.

This system traps nitrogen oxides, reducing toxic emissions. But the engine must regularly use more fuel to allow the trap to work. The car’s computer could save fuel by allowing more pollutants to pass through the exhaust system. Saving fuel is one potential reason that Volkswagen’s software could have been altered to make 11 million cars pollute more, according to researchers at The International Council on Clean Transportation.


Which Cars Are Affected?


The Environmental Protection Agency has said it will order Volkswagen to recall seven of its American car models with the affected engine type, for a total of about 500,000 vehicles. Volkswagen has not released a list of international models that have the same engine.

VOLKSWAGEN
Jetta
2009 to 2015

VOLKSWAGEN
Beetle and Beetle Convertible
2012 to 2015

VOLKSWAGEN
Passat
2012 to 2015

AUDI
A3
2010 to 2015

VOLKSWAGEN
Jetta SportWagen
2009 to 2014

VOLKSWAGEN
Golf
2010 to 2015

VOLKSWAGEN
Golf SportWagen
2015


The Emissions Tests That Led to Discovery of VW’s Cheating.


The on-road testing in May 2014 that led the California Air Resources Board to investigate Volkswagen was conducted by researchers at West Virginia University. They tested emissions from two VW models equipped with the 2-liter turbocharged 4-cylinder diesel engine. The researchers found that when tested on the road some cars emitted almost 40 times the permitted levels of nitrogen oxides.


The Newyork times.
http://www.nytimes.com/interactive/2015/09/22/business/international/vw-volkswagen-emissions-explainer.html?src=twr&smid=tw-nytimes&smtyp=cur&_r=0

It's a very sad issue..personally ,i believe other manufacturers are doing same..awareness will be increased henceforth..