Ford is revising the fuel economy label on its 2013 C-MAX Hybrid, changing it from the original 47 mpg city, highway, combined EPA rating to 43 mpg combined. The U.S. Environmental Protection Agency commented on this change, noting the ratings are 45 mpg city, 40 mpg highway, 43 combined.

Ford said the difference in mpg during testing versus what others claimed the C-MAX achieved on road was due to the larger effect that small differences in driving behavior and road conditions have on hybrids versus traditional gasoline-fueled vehicles.

The automaker added that since this change means a difference in estimated fuel costs,customers who purchased the vehicle will receive a check from Ford for $550. Ford said it will notify customers and that those with questions can visit Ford's site here or call 1-800-392-3673.

Looking ahead to the 2014-MY C-MAX, Ford said it will make a number of hardware changes to its 2014-MY C-MAX, including gearing changes that result in a more efficient transmission drive ratio; new parts designed to improve aerodynamics, including a new hood seal, new front and rear tire deflectors, new A-pillar moldings, and the addition of rear liftgate deflectors; and new engine oil with reduced friction. The automaker said testing for the 2014 C-MAX Hybrid isn’t complete.

Commenting on changes to the tests that resulted in the revised fuel-economy figures, the EPA said the agency tested the C-MAX after receiving complaints from consumers that the vehicle did not achieve the original estimated 47 highway, city, combined mpg as stated in the original tests. The EPA added that the label regulations, developed in 1977, don’t require vehicles with the same engine, transmission, and weight class to use the same fuel economy label value data since, historically, those families of vehicles typically achieved close to identical fuel economy performance.

EPA said newer vehicles, the C-MAX in this case, are more sensitive to small design differences that can affect fuel economy. In addition, the EPA noted that Ford’s hybrids are one of two examples in the industry where an automaker uses the same engine, transmission, and hybrid components across a number of vehicles. The EPA said with the new Ford C-MAX label, each vehicle design in the two high-efficiency hybrid families in the industry now has its own label.

The EPA said it plans to work with the industry, consumers, and environmental organizations to propose revised fuel economy labeling regulations.

Updated 8/16/2013, 9:14 am with commentary from EPA.