If you’ve ever wondered why a flock of motorcycles smells like a smog bomb made love to a junkyard, the secret is out. This week, Harley-Davidson agreed to pay $12 million in fines to the Environmental Protection Agency for evading clean air laws.

From 2008 to 2015, Harley-Davidson sold a device called a Screamin’ Eagle engine tuner (available in regular and pro variety), which allowed anyone to hack into their Hog’s emissions control software and dial it back to the simpler times of the 1950’s, when the kids were all excited about a hot new dance craze called the Twist, and America’s major cities were blanketed in a thick gray haze of Beijing-level air pollution.

As part of the settlement, Harley is required to stop making the tuners, to buy back and destroy all the ones currently for sale, and to spend $3 million on an as-yet-unspecified special project to reduce air pollution.

It’s no coincidence that Harley-Davidson was busted so soon after the Volkswagen emissions scandal, with the EPA taking a closer look at the so-called defeat devices auto companies have used to cheat emissions tests.

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Odds are good that Harley’s won’t be the only wheels on the road that will be forced to clean up their act.