Harley-Davidson has agreed to pay 15 million dollars (£11.4 million) to settle a complaint filed by US federal environmental officials over racing tuners that caused its motorcycles to emit higher than allowed levels of air pollution.
The Justice Department and the Environmental Protection Agency announced the settlement on Thursday.
According to documents filed in federal court, Harley-Davidson has manufactured and sold about 340,000 "Screamin' Eagle" tuners since 2008 that allowed users to modify a motorcycle's emissions control system to increase power and performance.
According to prosecutors, the "defeat devices" also illegally increased the motorcycles' emissions of such harmful air pollutants as nitrogen oxide.
The government said Harley-Davidson also made and sold more than 12,000 motorcycles of various models with the illegal tuners installed on them that were not certified as meeting clean air standards.