According to the report from The New York Times, it seems the cheating was done by installing software in its vehicles which will “render inoperative elements of the vehicle’s emission control system.” This means that the results will be different when it detects that the car is undergoing an emission test.
So how will the car know it’s undergoing an emissions test? The EPA states that this is done by “based on various inputs including the position of the steering wheel, vehicle speed, the duration of the engine’s operation, and barometric pressure.” In a statement released to ArsTechnica, a Volkswagen Group spokesperson confirm that the company has received the notice from EPA and are cooperating with their investigation.
According Cynthia Giles, the E.P.A.’s assistant administrator for the Office of Enforcement and Compliance, “Using a defeat device in cars to evade clean air standards is illegal and a threat to public health. Working closely with the California Air Resources Board, E.P.A. is committed to making sure that all automakers play by the same rules. E.P.A. will continue to investigate these very serious violations.”