DETROIT (AP) — Eleven people have been charged in Michigan in a scheme to evade air-pollution rules by tampering with software and hardware in heavy-duty diesel engines, federal authorities said Wednesday.

Nine of the 11 have agreed to plead guilty, along with three companies, according to documents filed in federal court in western Michigan.

Diesel Freak LLC, based in Gaylord, has agreed to pay a $750,000 fine. Accurate Truck Service, based in Grand Rapids, and a related company, Griffin Transportation, have each agreed to pay $500,000, court filings show.

Diesel Freak conducted remote engine reprogramming and counted Accurate Truck and Griffin Transportation as customers, authorities said.

Diesel engine modifications can "improve the horsepower, torque, fuel efficiency or other characteristics of diesel engines," the government said in the charging document. "These unlawful modifications result in a dramatic increase in multiple pollutants being emitted by each vehicle."

Diesel Freak rigged at least 362 vehicles, from 2015 to late 2018, and some "are still on the road," U.S. Attorney Mark Totten said.

"The vehicles involved in this scheme were fleet vehicles, which drove all over the country," said Henry Barnet, director of criminal enforcement at the U.S. Environmental Protection Agency. "Modified vehicles like these continue to pollute as long as they are in service."

Kevin Collins, an attorney for Diesel Freak, owner Ryan LaLone and employee Wade LaLone, had no immediate comment. The LaLones have agreed to plead guilty to conspiracy.

A message seeking comment was sent to the lawyer for Accurate Truck and Griffin Transportation.

The government said Diesel Freak used tools and emissions-cheating software developed by an Italian company and distributed in North America by an Ohio company, which was identified in court documents only as Company 2.

"The investigation is ongoing," Totten said.

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