The U.S. government is accusing Fiat Chrysler of failing to disclose software in some of its pickups and SUVs with diesel engines that allows them to emit more pollution than allowed under the Clean Air Act.
The Environmental Protection Agency is investigating whether the auxiliary emission control devices constitute "defeat devices," which are illegal because they turn off pollution controls.
If so, Fiat Chrysler may be liable for civil penalties.
The EPA says the software caused the vehicles to emit less pollution during testing than during regular driving.
And it says Fiat Chrysler hasn't provided any suitable explanation for why it failed to disclose the software.
The agency says it has issued a "notice of violation" to the company that covers about 104,000 vehicles including the 2014 through 2016 Jeep Grand Cherokee and Ram pickups, all with 3-liter diesel engines.
The California Air Resources Board took similar action.
Fiat Chrysler has issued a statement denying any wrongdoing.