WASHINGTON -- Don't blame the test.
That's the EPA's message in the wake of Ford Motor Co.'s decision to restate fuel economy estimates on its C-Max Hybrid.
When Ford C-Max owners were griping about worse-than-promised fuel economy last year, the conventional wisdom was that the EPA tests couldn't reliably measure the performance of hybrid cars.
Consumer Reports magazine stoked the fires, claiming that half the hybrids it tested fell short of their advertised mpg numbers by 10 percent or more. Ford chimed in as well, saying it would help the EPA figure out whether its tests were inflating the fuel economy estimates for many hybrids.
It was enough to make the EPA's own engineers question the accuracy of their tests, said Christopher Grundler, the agency's top auto industry regulator. But this summer, when the EPA ran the Toyota Prius and Hyundai Sonata hybrids through the same battery of tests that tripped up the C-Max, the other hybrids did fine.
"It was all quite reassuring," Grundler told Automotive News. "The problem here is really not how the testing is done."
Ford doesn't seem convinced. "This is an industrywide issue with hybrid vehicles," Raj Nair, the head of global product development for Ford, told reporters this month in announcing the C-Max restatement. "We've learned along with EPA that the regulations create some anomalies for hybrid vehicles under the general label rule."
According to the EPA, the C-Max had an inflated combined fuel economy estimate of 47 mpg because Ford used test results from the more aerodynamic Fusion Hybrid, which shares a powertrain with the C-Max and weighs about the same.
A decades-old rule allowed that approach to spare automakers the cost of redundant tests on nearly identical cars, such as the old Ford Taurus and Mercury Sable sedans.
But as cars became more efficient and automakers started selling more varied models with shared powertrains, the potential to mislead car buyers increased, Grundler said, and now the rule needs to change.
It should take the EPA less than a year to propose changes, he added, though the agency has given no timetable for a final rule.
Meanwhile, despite the urging of Consumer Reports, the EPA doesn't intend to rework its five-cycle fuel economy test. That test was revised in 2006 for the 2008 model year, in part because early hybrids were performing far better on the agency's test than in real life.
With those changes, the fuel economy of the Toyota Prius plummeted from 51 mpg highway and 60 mpg city to 45 mpg highway and 48 mpg city.
Though the EPA would not disclose the results of its tests this summer, owners now seem to be close to the 50 mpg that Toyota promises for the 2013 Prius in combined city and highway driving. Owners report an average of 48.4 mpg to the Web site fuelly.com and an average of 47.4 mpg on an EPA Web site, fueleconomy.gov.
Toyota -- which could have applied the Prius' 50 mpg rating to the larger, more wagonlike Prius V variant but decided not to -- is standing with the EPA.
"Toyota agrees with EPA that this is a not a hybrid issue, but strictly an issue of how the Ford C-Max Hybrid fuel economy values were determined," the company said in a statement.
"We believe the current labeling methodology established since 2006 provides appropriate fuel economy label values for customers, when automakers apply these rules with good common sense and engineering judgment."