The trouble is, the cleanliness of VW's four-cylinder diesels was an illusion. It took the International Council on Clean Transportation working with West Virginia University on a study carried out last year to discover that a diesel Jetta with the LNT was emitting up to 35 times the EPA's required limit on NOx, and a Passat fitted with a urea-based selective catalytic reduction, or SCR, system was emitting up to 20 times the limit. Threatened with a stop on its car sales, VW admitted that it had been using an illegal "defeat device" that understood when the car was being tested in laboratory conditions and activated an ultraclean mode.
The problem for VW was that cutting NOx is expensive. Analysts from Exane BNP Paribas estimate that reduction technologies have risen from around 700 euros ($790) per vehicle to meet Europe's Euro5 emissions targets to 1,300 euros for Euro6, which has just come into force this month. Neither of the two is as tough on NOx as the U.S.
"Diesel is more expensive than gasoline. Euro6 is even more expensive because it's very clean. So carmakers are not excited about launching Euro6," Renault-Nissan Alliance head Carlos Ghosn told journalists at the Frankfurt auto show this month.
The SCR after-treatment system, which requires top-offs of a urea solution and was adopted by Volkswagen for the Generation 2 versions of its BlueTDI, is considered better at reducing NOx, but it's more expensive and has additional problems. "SCR carries extra weight and servicing penalties. We want to avoid that for as long as possible," Uli Koesters, the Ford of Europe engineer in charge of the company's largest models, told Automotive News in March. Instead Ford will use the maintenance-free lean NOx trap for its 1.5- and 2.0-liter diesels in Europe.
The council on clean transportation in its initial study posited that the reason for the Passat's far-worse performance compared with a BMW X5 also fitted with an SCR system was because VW used less of the urea solution to reduce consumption and avoid frequent fills.
Volkswagen has said it also installed its dual-program defeat device in European models with the same EA 189 engine, but it's not thought to be active in all. "The European standards are easier to meet -- [so there's] less need to cheat," Bernstein Research analyst Max Warburton wrote in a note.