Shares of South Korea's largest carmaker Hyundai Motor and its affiliate Kia Motors plunged on Monday after they were found to have exaggerated the fuel efficiency of their vehicles sold in North America.
In mid-day trading, Hyundai Motor fell 7.4 percent to 199,000 won ($182), while Kia was down 7.1 percent at 56,200 won.
On Friday, the US Environmental Protection Agency said it had discovered inflated gasoline economy numbers on Hyundai and Kia models in an investigation sparked by consumer complaints.
The exaggerated numbers, which ran from one to six miles a gallon, had helped push some of the models into the much-vaunted 40 miles per gallon (MPG) club of gasoline-sipping vehicles.
The problem involved about 900,000 vehicles sold in the United States and 172,000 in Canada.
The two Korean companies blamed "procedural errors" and offered to reimburse car owners in both countries to cover the additional fuel costs associated with the MPG revision.