Renault has cheated for over 25 years on pollution tests for diesel and petrol engines with the knowledge of top management, according to a report by French fraud investigators.
"The entire chain of management" up to the French car maker's chief executive officer, Carlos Ghosn, was implicated in the "fraudulent strategies", said the report, which led prosecutors to open a probe into Renault in January.
Renault swiftly denied the accusations.
"Renault doesn't cheat," Thierry Bollore, the French car maker's second-in-command said, adding that all its cars complied with legal standards.
The report said there was no evidence of Ghosn having charged anybody else with approving the company's emissions control decisions, which therefore ultimately came under "his responsibility".
Police suspect the automobile maker of putting in place the strategies "with the objective of creating false results for antipollution tests", and so to be seen to be complying with European regulations.
The report concentrates on recent car models, but the fraud investigators – helped by statements by a former Renault employee – estimate that questionable practices have been in place since 1990.
Several Renault models were fitted with electronic devices which detected test conditions and then triggered a temporary reduction in harmful emissions for long enough to fool the testing equipment, the former employee claimed.
The first generation Renault Clio, which came out in 1990, is believed to be one of the models involved.
The alleged fraudulent practice recalls the "dieselgate" scandal involving Germany's Volkswagen which admitted in late 2015 to installing so-called "defeat devices" into 11 million diesel vehicles worldwide, designed to reduce emissions of harmful nitrogen oxides while the engines were undergoing regulatory tests.
(With inputs from PTI)