During a prolonged economic slump that has made Americans pinch their pennies even tighter, automakers have tried to sell consumers on the growing gasoline efficiency of their newest vehicles.
It turns out Hyundai and Kia sold the benefit a little too aggressively.
An audit released this week reveals the two Korean automakers significantly overstated the gas mileage -– by one to six miles -- on most of their U.S. models from the past three years.
The automakers must retrofit their windows stickers to lower the mileage estimate and could face additional penalties. And both have apologized and promised to compensate buyers for the differences in their gasoline bills for the life of their cars.
Nonetheless, Hyundai and Kia offer a cautionary tale that as automakers press to meet President Barack Obama's new 54.5 mile-per-gallon goal in 2025 consumers should be wary of window stickers that look too rosy to be true. At the very least, they should compare their consumption to the promise.
"Consumers rely on the window sticker to help make informed choices about the cars they buy," Gina McCarthy, assistant administrator of the EPA's air-quality office, said Friday. "EPA's investigation will help protect consumers and ensure a level playing field among automakers."
For misleading as many as 900,000 owners of cars and SUVs bought in the last three years, Kia and Hyundai win this week’s Whopper of the Week, a distinction awarded by the Washington Guardian for instances in which the public has been misled.
The investigation is the first in which erroneous test results were uncovered in a large number of vehicles from the same manufacturer. Only two similar errors have been discovered since 2000, and those involved single models, EPA said.
The EPA said it received about a dozen complaints from consumers that the mileage of their 2012 Hyundai Elantras didn't match the promise on the window stickers. That prompted EPA auditors to go out and check.
The audit turned up discrepancies between agency test results and data turned in by Hyundai and Kia, the EPA said. As a result, the automakers will have to knock one or two miles per gallon off the mileage posted on most of the models' window stickers. Some models will lose three or four miles per gallon, and the Kia Soul, a funky-looking boxy small SUV, will lose six mpg from the highway mileage on its stickers.
Hyundai and Kia are owned by the same company and share factories and research, but they sell different vehicles and market them separately.
The companies said the mistakes stemmed from procedural differences between their mileage tests and those performed by the EPA.
"We're just extremely sorry about these errors," said John Krafcik, Hyundai's CEO of American operations. "We're driven to make this right."
The changes affect 13 models from the 2011 through 2013 model years, including seven Hyundais and six Kias. Window stickers will have to be changed on some versions of Hyundai's Elantra, Sonata Hybrid, Accent, Azera, Genesis, Tucson, Veloster and Santa Fe models, as well as the Kia Sorento, Rio, Soul, Sportage and Optima Hybrid.
The Associated Press contributed to this article.