Well there is this here:

https://en.wikipedia.org/wiki/Defeat_device

In 1995, General Motors was ordered to recall 470,000 model year 1991 through 1995 Cadillacs and pay an $11 million fine for programming the car's electronic control unit (ECU) to enrich the fuel mixture any time the car's air conditioning or cabin heat was operating, since the EPA tests are conducted with those systems turned off.[10] The richer fuel mixture was needed to address an engine stalling problem, resulting in emissions of up to 10 grams per mile of carbon monoxide (CO), nearly three times the limit of 3.4 g/mi. While the EPA and Justice Department contended that GM intentionally violated emissions standards, GM said that was "a matter of interpretation." Besides the fine, the second largest Clean Air Act penalty to date in 1995, GM had to spend up to $34 million for anti-pollution programs and recall 470,000 Cadillac 4.9 liter Eldorados, Fleetwoods, DeVilles, and Sevilles.[10] The largest civil penalty under the Clean Air Act was $11.1 million paid by Louisiana-Pacific lumber and paper company.[10]

Sources are linked in the original article