The Environmental Protection Agency accused Fiat Chrysler on Thursday of installing software that appeared to enable certain diesel trucks to emit lower emissions during pollution tests. The company denied those accusations, saying its software meets regulatory requirements.

The vehicles involved were the 2014 to 2016 model year Dodge Ram 1500 pickup trucks and Jeep Grand Cherokees with 3.0-liter diesel engines. The allegations affect roughly 104,000 vehicles, EPA officials said.

The government says Fiat Chrysler failed to disclose that software in some of its vehicles allows them to emit more pollution than allowed. Associated Press/Carlos Osorio

Janet McCabe, head of EPA’s Office of Air and Radiation, said “no immediate actions are necessary” for owners because their vehicles are still safe and legal to drive.

The software reduced the amount of nitrogen oxide emitted during emissions tests, obscuring the fact that they spew more of the pollutant than is allowed under the Clean Air Act, officials said. They stopped short of calling the technology a “defeat device,” which is illegal, but said the company has not yet offered another explanation for the software.

The technology was brought to light after the EPA expanded its vehicle testing to look for so-called defeat devices in September 2015 following a similar scandal at Volkswagen. FCA did not disclose the software to regulators, which may itself be a violation of the law, the EPA said.

“Failing to disclose software that affects emissions in a vehicle’s engine is a serious violation of the law, which can result in harmful pollution in the air we breathe,” Cynthia Giles, assistant administrator for EPA’s Office of Enforcement and Compliance Assurance, said in a statement.

Fiat Chrysler officials denied those claims in a statement Thursday.

Every automaker must use “various strategies” to reduce tailpipe emissions without compromising the durability and performance of its engines, FCA said, adding its emission control system complies with necessary requirements.

The company also said it has offered to make extensive changes to its software to address EPA concerns.

“FCA U.S. intends to work with the incoming administration to present its case and resolve this matter fairly and equitably and to assure the EPA and FCA U.S. customers that the company’s diesel-powered vehicles meet all applicable regulatory requirements,” the company said in its statement.

Fiat Chrysler’s stock price dropped as much as 18 percent Thursday morning and trading was temporarily halted.

EPA officials said on a call Thursday that they are also looking into whether other automakers may be using similar devices.

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