By Allen L Phillips
In early 2014 the International Council on Clean Transportation (ICCT), a non-profit, contracted with West Virginia University's Center for Alternative Fuels, Engines and Emissions (CAFEE) to test Volkswagen 2.0 liter diesel engines. The stated purpose was to help convince European regulators to emulate strict U.S. standards for diesel emissions of nitrous oxides (NOx) although that does not explain why they structured the test they way they did.
Under the contract CAFEE rented VW diesel cars and measured tailpipe emissions on the road and compared that with emissions measured on the same cars in the lab, presumably under circumstances similar to a standard emissions test. (My question is why would they do the comparison unless they suspected something?)
In a standard emissions test a testing machine is connected to the car's diagnostic connector. The diagnostic connector is generally located under the dashboard and, in addition to emissions testing, is used to diagnose malfunctions in the various electronic control units in today's cars.