Hyundai, Kia Mileage Mishap: How It Happened

How did Hyundai-Kia get its estimated mileage ratings so wrong that it had to offer reimbursement to some 900,000 owners? The truth is complicated, and it gets to the complexities of EPA testing.

Hyundai-Kia's Sung Hwan Cho told reporters this morning that it's "a very complex testing process." Cho heads the automaker's U.S. technical centers. He shed some light on the EPA tests, which lead to the city and highway fuel-economy figures on a new-car window sticker. A key part of the tests involve measuring the resistance of various systems, dubbed the "road load" by engineers: how a car's tires meet the pavement, how the vehicle's shape cuts through the air and how the drivetrain's moving parts work in tandem. Each area translates to fuel efficiency, or lack thereof.

"There are hundreds of different parameters that can affect this road load," Cho said. "Ambient temperature, wind speeds, atmospheric pressure."

Then there's a litany of variations within each test vehicle — how many miles are on it, the condition of the drivetrain, the tire wear. Finally, the test procedures themselves involve "which kind of regulation and guidance procedures you follow, and how you process the data, and how you calibrate your measurements," he said.

Somewhere in those variations, Hyundai-Kia went askew of EPA guidance. But exactly how much guidance exists is up in the air.

What to Do If You Own an Affected Hyundai, Kia

We reported this morning that Hyundai and Kia are revising gas mileage ratings for nearly 900,000 vehicles from the 2011 through 2013 model years — about a third of the cars sold by the affiliated Korean automakers over that range. 

What does it mean to you if you own one of the affected cars? We just got off the line with Hyundai and Kia officials, and here are some answers:

Cars.com's Mileage Tests of Hyundai and Kia Vehicles In Line With EPA Results

In the wake of today's news that Hyundai and Kia will reimburse owners for bad mileage estimates, we've compiled the results of our mileage tests from Shootouts and other challenges we've conducted over the past few years that involved the affected cars and SUVs.

In September 2011, we took the previously 40-mpg-rated Hyundai Elantra and pitted it against special "fuel-saving" trims from the competition designed to eke out a few mpgs more to hit that vaunted 40 mpg highway figure. The Elantra's new highway rating is 38 mpg, and its combined rating dropped to 32 mpg from 33.

Our results put the Hyundai in last place.

Hyundai, Kia to Pay 900,000 Owners for Bad MPG Estimates

Hyundai and Kia announced today they would reimburse owners of about 900,000 vehicles for misstated mileage ratings.

The news came after an investigation by the EPA into complaints from consumers that the two companies' mileage claims were inflated. As a result, the stated mpg ratings for 75 different trim levels over three model years will be changed, and window stickers of cars on sale will be replaced to reflect the new numbers.

Cars.com's Mileage Tests of Hyundai and Kia Vehicles In Line With EPA Results

The investigation began when the EPA received complaints from owners of the 2012 Hyundai Elantra compact sedan who said that they were not seeing gas mileage near the stated numbers. Once the EPA’s investigators confirmed a discrepancy, they broadened the audit to the rest of the vehicles.

Hyundai and Kia are owned by the same parent company in South Korea but operate separately in the U.S. Both have seen phenomenal growth in the past few years, not just because of improved styling and quality, but also for their exceptional fuel economy.

The changes affect the 2011-2013 model years with mileage ratings dropping from 1 to 6 mpg on the highway. Combined mileage ratings were more accurate with seven of the 43 Hyundai models and four of the 32 Kia models seeing no change in combined mileage after the audit. Twenty-four of the 43 Hyundais showed a difference of 1 mpg combined, while 11 of the 32 Kias were within 1 mpg of the original rating.

The company explained the error this way: "The fuel-economy rating discrepancies resulted from procedural errors during a process called 'coastdown' testing at the companies’ joint testing operations in Korea. Coastdown testing simulates aerodynamic drag, tire rolling resistance and drivetrain frictional losses and provides the technical data used to program the test dynamometers that generate EPA fuel economy ratings."

The two brands will announce a reimbursement program for current and former owners of the vehicles. A personalized debit card will be issued that will calculate the difference based on fuel prices and miles driven, plus 15% as a mea culpa from the automakers.

Will it be enough to satisfy consumers? That’s a question that will be asked nationwide as owners digest the news.

Below are the breakdowns of every vehicle impacted in the change, provided to Cars.com by Hyundai/Kia. We’ll have much more on this story as it develops throughout the day and coming weeks. If you have a question you’d like answered, leave it in the comments below or email us at editor@cars.com.