The EPA has ordered Kia and Hyundai to amend window stickers on 13 models from the 2011, 2012 and 2013 model years after the two companies were found to be misstating the cars' true efficiency.
The companies will also have to pay damages to 900,000 owners across the U.S.
According to Associated Press (via our sister site, TheCarConnection), the models were red-flagged after customers found they were struggling to get anywhere near the official fuel figures on several cars.
Vehicles featuring EPA sticker discrepancies include the Hyundai Accent, Azera, Elantra, Genesis, Santa Fe, Sonata Hybrid, Tucson and Veloster. Kia vehicles which require re-stickering include the Optima Hybrid, Rio, Sorento, Soul and Sportage.
The figures for most vehicles will change by only 1 or 2 mpg in certain measurements. Others, like the Soul, will lose up to six miles per gallon.
Compensation will depend on just how far out the stated efficiency was. Owners will be paid a rate based on how far they've driven the vehicle since buying it new, multiplied by how much less they would have spent on gas in that time, plus a 15 percent premium.
Kia's Michael Sprague says a car with a 1 mpg discrepancy and 15,000 miles on the odometer would receive $88.03 in compensation, including the 15 percent. A Kia Soul, out by 6 mpg and with several thousand more miles on the odometer, could be in line to receive a large amount of money.
Both companies have apologized unconditionally for the errors, and blame an administrative and procedural error, rather than deliberate intention.
Window stickers on new Hyundais and Kias have already been changed.