The companies said in a release that 172,000 cars across Canada are affected.
On average, the fuel consumption across all Kia and Hyundai cars is actually 0.3 litres higher per 100 kilometres than advertised — meaning if your car allegedly can go 100 kilometres on 10 litres of gas, chances are it will actually use 10.3 litres to do that trip.
Both companies have implemented a comprehensive reimbursement program to any current or former owners of the cars in question.
Owners will get a credit card loaded with cash to cover the extra fuel they have had to buy. How much the card will have on it is based on the average fuel price where they live, and how much the car was driven.
Drivers will get gas card
Drivers will also get a 15 per cent top-up to compensate them for the inconvenience, the companies say.
"We are very sorry about the errors and we are committed to making sure the owners of every affected Hyundai vehicle are fully compensated," Hyundai Canada CEO Steve Kelleher said.
"Kia Canada deeply regrets that this situation has occurred and will ensure all affected Kia customers will quickly receive fair compensation," Kia Canada CEO William Lee added.
The companies say the fuel consumption rating discrepancies came from procedural errors during a process called "coast down" testing at joint testing operations in Korea.
The move came about as a result of an investigation from the U.S. Environmental Protection Agency. The agency says their investigation is ongoing, but won't comment on whether any additional fines might be forthcoming.