DETROIT -- Hyundai and Kia overstated the gas mileage on 900,000 vehicles in the past three years, a discovery that could result in sanctions from the U.S. government and millions of dollars in payments to car owners.
The inflated figures were uncovered by the Environmental Protection Agency in an audit of gas mileage tests by the two South Korean automakers. The agency, which monitors fuel economy, said Friday it's investigating how the companies came up with their numbers.
The EPA found inflated gas mileage on 13 models from the 2011 through 2013 model years, including Hyundai's Elantra and Tucson, and Kia's Sportage and Rio. The sticker mileages were overstated on about one-third of the cars sold by the companies during the three years.
As a result, Hyundai and Kia will have to knock one or two miles per gallon off the vehicle stickers of most of their models. Some models will lose three or four miles per gallon. The Kia Soul, a funky-looking boxy small sport utility vehicle, will lose six from its highway figure, lowering it from 34 mpg to 28 mpg.
"Consumers rely on the window sticker to help make informed choices about the cars they buy," said Gina McCarthy, assistant administrator of the EPA air-quality office. "EPA's investigation will help protect consumers and ensure a level playing field among automakers."
The agency would not comment when asked if the companies will be fined or if a criminal investigation is under way. Hyundai and Kia are owned by the same company and share factories and research, but they sell different vehicles and market them separately.
The reduced mileage figures are a black eye for the companies, which have seen explosive sales growth in the United States partly because of advertising campaigns touting gas mileage. Hyundai even poked fun at competitors who promoted special high-mileage versions of their cars, claiming its cars had high mileage across the model lineup.
The EPA said it's the first case in which erroneous test results were uncovered in such a large number of vehicles from the same manufacturer.
Company executives apologized for the discrepancies and promised to compensate customers because they're using more gasoline than expected. The executives said the higher mileage figures were unintentional, caused by errors in following EPA mileage test procedures. The customer payments are likely to cost Hyundai and Kia millions of dollars.
Michael Sprague, executive vice president of marketing for Kia Motors America, said the companies have a program to reimburse customers.
Dealers will find out how many miles the cars have been driven and figure out the increased cost to owners due to the lower gas mileage.