Ford today lowers the fuel economy ratings on six vehicles, including ’13-’14 Ford Fusion and C-Max hybrids and plug-in hybrids, the Lincoln MKZ hybrid and most versions of the Fiesta.

The automaker says it will compensate owners for the fuel cost difference. The drop in the C-Max fuel-economy rating marks the second time Ford has taken such action on that vehicle, first lowering the figure last year.

“We’re committed to offering top fuel economy and accurate information for our customers,” Raj Nair, group vice president-Global Product Development, says in a conference call with reporters. “We do everything possible to make sure that’s the case.”

Nair says the automaker identified an error with its fuel-economy ratings on certain vehicles through its internal testing and notified the EPA. The error was specific to a factor called Total Road Load Horsepower, which is a vehicle-specific resistance level used in vehicle dynamometer testing that determines fuel economy ratings.

“There was an update to our (TRLHP) model done at a time when these vehicles were in development,” he says. “Also, hybrids are very sensitive to TRLHP relative to fuel economy, so we retested vehicles that were affected.”

In most of the models involved, fuel-economy ratings drop by 1-2 mpg (100-50 km/L). The largest discrepancy is with the Lincoln MKZ hybrid, which sees its EPA rating drop 7 mpg (14.2 km/L), from a previously combined city/highway rating of 45 mpg (5.2 L/100 km) to 38 mpg (6.1 L/100 km).

“The MKZ was more affected by the changes in TRLHP because of weight, aerodynamics and tire differences,” Nair says. “It will affect different vehicles differently.”

Ford estimates 200,000 of the vehicles have been sold or leased to customers in the U.S., with 13,000 more in Canada and several thousand in surrounding territories.

Affected customers will receive a goodwill payment for the estimated average fuel costs of the difference between the two fuel economy labels, with payouts ranging from $150 to $1,050, depending on whether the vehicle was leased or purchased.

Nair says the error first was noticed in March, and the automaker began working with the EPA to rectify it. The issue, he says, was due to mistakes made by Ford’s product-development team, which he leads.

“There was no intent to mislead on anyone’s part,” he says. “Nevertheless, it was a mistake in product development and that responsibility lies with me.”