The PSA Group, parent company of Peugeot, Citroën and DS, has been accused of using illegal emissions cheat software in Euro 5-spec diesel vehicles.

According to reports in French newspaper Le Monde, “at least" 1,914,965 diesel vehicles could be affected by the software.

If true, PSA could be subject to fines totalling about €5 billion. It would embroil PSA in a diesel emissions scandal that first came to light in 2015 with Volkswagen's Dieselgate case.

The claims against PSA are published in a report from the European Union’s directorate-general for competition, consumer affairs and fraud prevention. PSA said it had not previously had access to the report and so was unable to respond to the specific claims.

"[PSA] complies with regulations in every country where it operates and its vehicles have never been equipped with software or systems making it possible to detect compliance tests and to activate a pollutant treatment device that would be inactive during customer use," the company said in an official statement.

"[PSA] is the only car manufacturer in the world to have put in place a total transparency approach regarding the consumption and CO2 emissions of its models in real use conditions. This approach will be extended to nitrogen oxide emissions by the end of 2017. The results of the 400 measures covering 60 models (80% of European sales) are available on the brands’ websites."

PSA has now reserved the right to file a complaint for breach of confidentiality.

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