The stock was repeatedly suspended from trading on the Milan bourse after it shed by as much as 16 per cent. Just before 1600 GMT it was showing a loss of 15.7 per cent at 8.83 euros.
On Wall Street, where the stock is also listed, it fell by 12.9 per cent.
The Environmental Protection Agency said the undisclosed software on the 2014 to 2016 models of Grand Cherokees and Dodge Ram 1500 trucks sold in the United States allowed the vehicles to emit more nitrogen oxides than permitted.
Just the day before, US officials said that German rival Volkswagen would plead guilty to three criminal charges and pay a total USD 4.3 billion in fines to settle a much bigger emissions cheating scandal, known as "dieselgate".
The US Justice Department charged VW with conspiracy to defraud the United States and violate the Clean Air Act for using defeat devices on its diesel vehicles that evaded emissions standards.
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