After federal testing, BMW will have to reduce fuel mileage claims on four of its Mini Cooper models, the fourth such action in two years by an automaker.

The discrepancy was discovered during testing at the Environmental Protection Agency's lab in Ann Arbor, Mich., according to an Associated Press report.

The reduced fuel economy affects the 2014 Mini Cooper three-door and Mini Cooper three-door S versions equipped with manual and automatic transmissions for highway, city and combined driving.

The biggest mileage cut is for the S model with a manual transmission, which will go from 38 miles per gallon in highway driving to 34 mpg and 25 mpg city driving to 24.

In the past two years, Hyundai-Kia, Ford and Mercedes-Benz have also been found to have overestimated gas mileage while doing their own fuel economy estimates. Automakers use EPA testing guidelines to calculate fuel mileage, and some claims are found to be overstated during EPA audits.

The agency is working to boost its auditing efforts in the wake of these overstated fuel economy incidents.

"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, as quoted by the AP.

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