Last Updated Oct 22, 2014 3:16 PM EDT
DETROIT - The U.S. government has told BMW to reduce the gas mileage estimates on the window stickers on four of its Mini Cooper models after an audit found the figures were overstated.
The discrepancy, which varies from one to four miles per gallon depending on model, was discovered in testing at the Environmental Protection Agency's lab in Ann Arbor, Michigan, the agency said in a statement Wednesday.
The reductions affect the 2014 Mini Cooper three-door and Mini Cooper three-door S models with manual and automatic transmissions. The biggest discrepancy was in highway mileage, but city and combined mileages also must be reduced.
It's the fourth time in the past two years that the EPA has found that an automaker overstated gas mileage test results. The automakers do their own estimates based on testing guidelines from the EPA. Hyundai-Kia, Ford and Mercedes-Benz all had to reduce mileage estimates on some of their models as the EPA increased its auditing efforts.
"To provide consumers with the most accurate, reliable and repeatable fuel economy values, we are continuing to strengthen our oversight to ensure fair competition among automakers," said Christopher Grundler, director of the EPA's Transportation and Air Quality office.
With the Mini Coopers, the biggest reduction will come from the S model with a manual transmission. BMW will have to cut the highway mileage estimate from 38 mpg to 34 mpg. City mileage for the same model gets shaved by one mpg from 25 to 24.
A Mini spokesman said in a statement that new labels for in-stock 2014 models have been sent to dealers. The mileage estimates were changed after the EPA tested one model and got different results, the statement said. Mini engineers worked with the EPA to incorporate agency findings into Mini's computer simulation testing, the statement said.
BMW's mileage estimates were higher than the EPA's because the company's figures for wind drag, tire rolling resistance and engine-transmission friction were lower than those calculated by the agency, a spokeswoman said in an e-mail. She wouldn't say if the error was intentional or not, but said the EPA's Office of Enforcement will determine if further investigation is needed.