A few years ago, engineers at a Detroit automaker tested and then took apart a diesel-powered Volkswagen Jetta, trying to figure out how the car could meet stringent U.S. environmental standards without an expensive selective catalytic reduction system to help neutralize its emissions.
They were flummoxed.
They couldn't duplicate the claimed EPA emissions test results on the road.
But that is as far as it went. The automaker's emissions and fuel economy experts didn't dig into the electronic control module that manages the Jetta's engine and emissions system.
If they had, they might have learned that the Jetta, like 11 million other VW diesels around the world, had software that allowed it to switch to a test mode during laboratory emissions tests, then switch to a different mode when driving, a mode that caused the car to emit as much as 40 times the legal limit of oxides of nitrogen, or NOx.
Were there other warning signs that could have tipped off regulators that Volkswagen diesels driven on the road were polluting too much?
There were a few, but they were hard to spot, and no one linked them until researchers and regulators began putting the clues together last year.
- Launch delay: Volkswagen, in late 2007, announced a delay of its new generation of diesel engines by six months because of unspecified emissions compliance problems. VW said it had a fix that would require the new diesels to be recertified. VW didn't offer a diesel engine in the 2007 and 2008 model years. The diesels arrived in August 2008.
- Competitors' struggles: Several other automakers, such as Honda and Nissan, announced plans for diesel cars or light-duty trucks in the U.S., but then canceled them. Honda was expected to launch a diesel in the Civic and CR-V in 2009. Nissan announced in 2007 that it planned to offer a diesel-powered Maxima by 2010. Toughening California emissions standards, falling fuel prices and the added expense of diesel emissions equipment sank Nissan's plans. Ford and GM also canceled plans for small diesel engines in their pickups. The cost of emissions controls was one factor. More recently, Mazda has been trying to certify a diesel engine for its Mazda6 sedan but has been wrestling with a host of emissions problems. Why was VW the only company that could offer affordable diesel-powered cars that hit emission targets?
- Fuel economy: On the EPA's fueleconomy.gov website, VW diesel owners routinely reported getting higher fuel economy than the EPA window label number. That's not unusual for a diesel-powered car. But many of the reported numbers have been 10 mpg or more than the window sticker. That's a red flag, says Nick Molden, CEO of Emissions Analytics, a Winchester, England, company that tests vehicles for emissions and fuel economy.
Here's why: The emissions system in the affected 2009-14 U.S. diesel cars are tuned to periodically run "rich" -- that is, to use more fuel than necessary. The rich fuel-air mixture cleans the oxides of nitrogen that builds up in the NOx trap in the car's exhaust system. The higher fuel economy reported by drivers suggests that the engines weren't running rich enough to enable the lean NOx trap to do its work, Molden says.
- Air quality: Despite decadeslong initiatives to clean the air in Europe, smog remains a major problem in cities such as Paris and London. In March 2014, the smog was so bad in Paris that the city government banned certain vehicles from city limits for nearly a week.