Why Volkswagen Cheated with their Diesel Engine

The engine cheat code scandal happened because Volkswagen (VW) is one of the biggest champions of diesel engines. 'Clean diesel' engines was how it planned to achieve its objective of becoming the world's largest car maker. This demanded a huge growth in North America, a market with strict rules regarding engine power, emissions standards, and fuel economy. But VW's engineers could not meet the twin goals of delivering both, a good fuel economy & low emissions and so they cheated.

What they did.

Most cars today including VW's cars have engines controlled by computer chips for optimum performance. VW added some software code so that the controllers of their 2.0-liter turbo diesel engines would recognise the protocols of the EPA's FTP-75 test. The controllers would then recalibrate the engine to reduce oxides of oxygen when undergoing testing thus ensuring that the engine was US EPA Tier 2 compliant. The controllers would revert the engine to its normal working parameters when it sensed the car was back on-road.

The EPA’s Tier 2 Test set extremely tough requirements, cutting allowable oxides of nitrogen by 83% over Tier 1 regulations. VW could have used Selective catalytic reduction (SCR), which involves spritzing small amounts of urea and water into the exhaust stream to facilitate the breakdown of NOx into nitrogen and carbon dioxide. But that meant reengineering cars like the Jetta & Golf popular in the US. So with the Tier 2 deadline looming in 2007, VW was faced with the prospect of spending millions on an aging product in the American market where just 0.2 percent cars were diesels.

So in 2009, out comes a totally compliant Jetta TDI model. It took care of emissions with an underfloor NOx trap, in which NOx is captured, then converted to nitrogen and carbon dioxide via occasional spurts of diesel fuel. It didn’t work quite as well as SCR, but it was a lot easier and cheaper to retrofit.  The advertised city and highway figures of 30 and 41–42 mpg (depending on the transmission) showed the engine to be very fuel-efficient. Its just that the engine was programmed to squirt less fuel into the exhaust when the car was on the road, allowing more NOx out of the tailpipe and raising mileage.

Tough NOx standards with Euro 6 regulations would come into effect in Europe (the market that VW dominates and has 55% diesel passenger cars) only in 2014.  VW engineers must have thought that they would go with the cheat code only until 2014, by which time better NOx-reducing technology would be incorporated through normal platform updating. Why VW would continue to include the cheat code in engines built in 2014 and later is the billion dollar question.