According to letters sent to VW on Sept. 18, 2015, from the Environmental Protection Agency and the California Air Resources Board, here’s a deeper dive on what happened. When the EPA conducts emissions testing, automakers have to disclose “auxiliary emissions control devices,” according to the EPA’s letter. These AECDs affect a car’s emissions system based on situational factors, such as how hard the engine is running or how hot it is. The EPA calls AECDs “defeat devices” only if they reduce the effectiveness of emissions controls outside of testing parameters and are not necessary for safety or engine startup.
Mid-2000s: The problem begins when VW decides to push for diesels in the U.S. in 2005. In developing its EA189 four-cylinder diesel — the basis for both the Generation 1 and Generation 2 diesel engines later cited for emissions cheating — a group of powertrain employees decides that by changing “only a small number of an approximate total 15,000 individual algorithms” in the engine management software, the diesel engines could meet emissions targets “within the budget that was available for the development of the engine management software and without the need to involve superior levels,” according to a statement by VW in 2016.
May 2014: Researchers at West Virginia University and the International Council on Clean Transportation publish findings that find “significantly higher in-use emissions” in a 2012 Jetta TDI and 2013 Passat TDI, according to the EPA. (Volkswagen markets its diesel cars as TDI.) Volkswagen tells regulators that the differences amount to technical issues and “unexpected” test conditions. Volkswagen sends then-CEO Martin Winterkorn a notice regarding the ICCT testing, but it’s bundled with his weekend memos. It’s unclear how much attention it receives.
December 2014: Volkswagen agrees to voluntarily recall its diesel cars to address the emissions issues by recalibrating its first- and second-generation EA189 diesel engines.
May 2015: CARB tests the updated emissions on a 2012 Passat TDI, in a lab and on the road. The agency finds some improvement, but not enough.
July 2015: On July 8, CARB shares its findings with VW. None of the technical issues suggested by the automaker are found to explain CARB’s results. Between July 8 and Sept. 3, CARB and the EPA say they will not certify VW’s 2016 diesel lineup, a necessary step to put those cars on sale. Only then does VW admit to software irregularities. The automaker discloses that the software calibrations in three separate diesel emissions systems had “a second calibration intended to run only during certification testing,” according to CARB.
Sept. 3, 2015: VW admits that the cars were “designed and manufactured with a defeat device to bypass, defeat or render inoperative elements of the vehicle’s emission control system,” CARB says.
The software uses “dyno” and “road” calibrations that read when an emissions test is being conducted; when the car is not being tested, the “road” calibration dials back the effectiveness of two types of emissions-treatment systems: nitrogen oxide traps and selective catalytic reduction (a urea solution). When dialed back, the systems allow the engine to emit nitrogen oxide levels that are 10 to 40 times the allowable amount by the EPA.