Here's the summary for the wikipedia article you mentioned in your comment:

The Volkswagen emissions scandal, sometimes known as Dieselgate or Emissionsgate, began in September 2015, when the United States Environmental Protection Agency (EPA) issued a notice of violation of the Clean Air Act to German automaker Volkswagen Group. The agency had found that Volkswagen had intentionally programmed turbocharged direct injection (TDI) diesel engines to activate their emissions controls only during laboratory emissions testing, which caused the vehicles' NOx output to meet US standards during regulatory testing. However, the vehicles emitted up to 40 times more NOx in real-world driving. Volkswagen deployed this software in about 11 million cars worldwide, including 500,000 in the United States, in model years 2009 through 2015.

^article^ ^|^ ^about^