DETROIT (AP) — A change in pollution control hardware between model years cut the gas mileage on some General Motors SUVs and forced it to correct the figures on window stickers, the company said Wednesday.
GM announced last week that the fuel economy was overstated by one-to-two miles per gallon on the 2016 GMC Acadia, Chevrolet Traverse and Buick Enclave.
But Consumer Reports magazine questioned why the 2016 mileage would be worse than the 2015 models when little was changed between model years and the SUVs from each year had the same engines and transmissions.
GM spokesman Nick Richards said Wednesday he doesn't know why the pollution hardware was changed. But he said the SUVs from all model years comply with clean air laws. The mileage was recalculated for 2016 but never made it onto the window stickers, he said.
The mistake was discovered recently by engineers who were working on the 2017 model stickers. The company said the mistake was inadvertent and that it informed the U.S. Environmental Protection Agency.
GM now is in the process of tracking down 170,000 owners of 2016 models to give them new stickers, Richards said. It's likely that they'll get some money, too. In similar cases automakers including Hyundai and Kia compensated owners for the difference in window sticker mileage estimates.
Jake Fisher, Consumer Reports' auto testing chief, said GM's explanation still doesn't make sense. He said he's not aware of any change in pollution control standards that would require any hardware change and that it's rare for a company to make such alterations between model years.
"If they changed that car for pollution reasons and the 2015s passed pollution controls, I don't understand why they would do that and cut fuel economy by 10 percent," Fisher said.
EPA spokeswoman Laura Allen deferred comment on the mileage to GM and didn't answer questions about whether the agency is investigating. But Richards said GM employees "continue to work with the EPA on this issue."
GM told dealers to stop selling the roughly 60,000 of the SUVs on their lots until new stickers could be printed. Richards said most dealers now have the new stickers and can resume sales once they're glued to the windows.
For a front-wheel-drive version, the 2016 fuel economy of the SUVs was revised to 15 mpg city, 22 mpg highway and 18 mpg combined. The 2015 models got 17 mpg in the city, 24 on the highway and 19 combined.