The Wall Street Journal reported Monday the discrepancies between the official gas mileage ratings for the Ford Fusion and C-Max wagon hybrids and the Consumer Reports data had sparked the probe.
Officially, the fuel efficiency for both the hybrid Fusion sedan and the C-Max wagon is listed at 47 miles per gallon overall, the Journal said.
But Consumer Reports tests found the Fusion and C-Max were achieving 39 miles per gallon and 37 miles per gallon, respectively.
"We feel confident that we have handled [efficiency testing] in the manner prescribed by the EPA," said Raj Nair, Ford's global vice president of product development.
Nair also said the C-Max hybrid's rating is dependent on driving no faster than 62 miles per hour when it runs on electricity alone. "Electric mode only up to 62 mph certainly helps us on the EPA cycle," he said.