According to both carmakers there was a mistake with the numbers due to "Procedural errors at the automakers’ joint testing operations in Korea". Because of these errors approximately 900.000, or 35 percent of, 2011-13 model year vehicles sold until October 31, 2012. 600.000 from Hyundai and 300.000 Kia models.
So now both brands are going to compensate the owners of the affected vehicles with the value of the difference between the old value and the new one and the number of kilometers the car has driven, plus an extra 15%.
“Given the importance of fuel efficiency to all of us, we’re extremely sorry about these errors,” “When we say to Hyundai owners, ‘We’ve got your back,’ that’s an assurance we don’t take lightly. We’re going to make this right for everyone, and we’ll be more driven than ever to ensure our vehicles deliver outstanding fuel economy.” said John Krafcik, president and CEO of Hyundai Motor America.
The affected models are the following and is only applied to the USA:
Kia
2011
Optima HEV
2012
Rio
Sorento
Soul
Soul ECO
Sportage
Optima HEV
2013
Rio
Sorento
Soul
Soul ECO
Sportage
Hyundai
2011
Elantra
Sonata HEV
2012
Accent
Azera
Elantra
Genesis
Sonata HEV
Tucson
Veloster
2013
Accent
Azera
Elantra
Elantra Coupe
Elantra GT
Genesis
Santa Fe Sport
Tucson
Veloster
Source: Kia and Hyundai