Ford yesterday announced that it was re-stating the fuel economy label of the C-Max hybrid, from 47 city / 47 highway /47 combined to a still very good but not as impressive 45city / 40highway / 43combined. Note the large decline in the highway number.
So what happened? Did Ford cheat the test? Not really.
What happened was that Ford used the Fusion Hybrid test results to certify the C-Max, which they are allowed to do according to EPA regulations. The EPA regs allow manufacturers to certify vehicles as a group if they are in the same weight class and share powertrains.
Here is the EPA's short report on the matter. An excerpt:
Ford based the 2013 Ford C-Max label on testing of the related Ford Fusion hybrid, which has the same engine, transmission and test weight as allowed under EPA regulations. For the vast majority of vehicles this approach would have yielded an appropriate label value for the car, but these new vehicles are more sensitive to small design differences than conventional vehicles because advanced highly efficient vehicles use so little fuel.
In this case, EPA's evaluation found that the C-Max's aerodynamic characteristics resulted in a significant difference in fuel economy from the Fusion hybrid.
Was this intentional, a case of Ford using the higher number for marketing purposes? Or was it a case of simply not knowing that the C-Max would test out so much differently? I have no idea. But I think in the future, Ford and other carmakers are going to be more careful about publishing fuel economy numbers based on assumptions, after this PR disaster.