Harley-Davidson has agreed to pay 15 million dollars (£11.4 million) to settle a US government complaint over racing tuners that caused its motorcycles to emit higher-than-allowed levels of air pollution.
Harley-Davidson manufactured and sold about 340,000 Screamin' Eagle Pro Super Tuners since 2008 that allowed users to modify a motorcycle's emissions control system to increase power and performance, according to court filings by the Justice Department and Environmental Protection Agency (EPA).
The "defeat devices" also illegally increased the motorcycles' emissions of such harmful air pollutants as nitrogen oxide, prosecutors said.
The government said Harley-Davidson also made and sold more than 12,000 motorcycles of various models with the illegal tuners pre-installed on them that were not certified as meeting clean air standards.
The Milwaukee-based company said the tuners in question were designed for use on specialised track racing bikes and not intended for use on public roads.
"This settlement is not an admission of liability but instead represents a good faith compromise with the EPA on areas of law we interpret differently," said Ed Moreland, Harley-Davidson's government affairs director.
"For more than two decades, we have sold this product under an accepted regulatory approach that permitted the sale of competition-only parts. In our view, it is and was legal to use in race conditions in the US."
Under the agreement, Harley-Davidson said it will no longer sell the racing tuners. The company said it will still sell a different model designed to comply with state and federal clean air standards.
Harley-Davidson will also pay a 12 million dollar (£9.1 million) civil penalty and spend three million dollars (£2.3 million) to mitigate air pollution through a project to replace conventional woodstoves with cleaner-burning versions.
"This settlement immediately stops the sale of illegal after-market defeat devices used on public roads that threaten the air we breathe," said Cynthia Giles, assistant administrator of EPA's enforcement arm.
"Harley-Davidson is taking important steps to buy back the 'super tuners' from their dealers and destroy them, while funding projects to mitigate the pollution they caused."