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

` From 2014 onwards, software which manipulated air pollution tests was discovered in vehicles from some car makers; the software recognized when the standardized emissions test was being done, and adjusted the engine to emit less during the test. The cars emitted much higher levels of pollution under real-world driving conditions. Some cars’ emissions were higher even though there was no manipulated software. Scandals relating to higher-than-reported emissions from diesel engines began in 2014 when the International Council on Clean Transportation (ICCT) reported discrepancies between European and US models of vehicles. This began with the Volkswagen emissions scandal. Independent tests carried out by the German car club ADAC proved that, under normal driving conditions, diesel vehicles including the Volvo S60, Renault’s Espace Energy and the Jeep Renegade, exceeded legal European emission limits for nitrogen oxide (NOx) by more than 10 times. ICCT and ADAC showed the biggest deviations from Volvo, Renault, Jeep, Hyundai, Citroën and Fiat.Researchers have criticized the inadequacy of current regulations and called for the use of a UN-sanctioned test called Worldwide harmonized Light vehicles Test Procedures that better reflects real-life driving conditions. The test only came into force in 2017, with critics saying that car firms lobbied fiercely to delay its implementation due to the high cost of meeting stricter environmental controls.Conservative Internal Market spokesman Daniel Dalton – who led the legislation through the European Parliament – described the previous regulations as “at best patchy and at worst ineffective.” He further said that his latest 2018 report introduced a strong, transparent system to ensure cars are safe and meet emissions standards.

Since 2016, 38 out of 40 diesel cars tested by ADAC failed a NOx-test. `

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