Just as Volkswagen cleans up the remnants of its dirty diesel scandal, the folks at Fiat Chrysler find themselves on the receiving of a lawsuit brought by the Environmental Protection Agency and the Justice Department accusing the carmaker of rigging its own diesel engines to fool emissions tests.

The EPA, along with the California Air Resource Board determined earlier this year that FCA was using so-called “defeat devices” that allow a car to pass emissions tests in a garage but spew potentially illegal levels of toxins into the air when on the road.

Today’s lawsuit [PDF], filed in a federal court in Detroit, alleges that 104,000 FCA vehicles with 3.0 liter EcoDiesel engines (specifically Ram 1500 trucks and Jeep Grand Cherokees, model years 2014-2016) are equipped with software that was not disclosed to the EPA when FCA applied for certificates of conformity (COC) — documentation required by the Clean Air Act indicating a car meets minimum emissions standards.

This software, notes the complaint, used a number of factors — like vehicle speed and coolant temperature — to determine when and when not to turn on the car’s emissions control systems. It could allegedly detect when these Ram or Jeep Cherokee vehicles were being tested, thus turning the control systems on so the vehicles produced “emission results that are compliant with emission standards.” This same software “cause[d] the emission control system to underperform or shut off” under normal vehicle operation.

For example, when a vehicle was determined to be moving at full highway speed, it would completely halt the process known as Exhaust Gas Recirculation, which is intended to reduce nitrogen oxide (NOx) emissions by recirculating a portion of the exhaust gas to the combustion chamber, reducing the formation of NOx in the engine. However, this was apparently no longer happening once these Ram and Jeep vehicles hit full speed.

Vehicles are allowed to have software and other devices that adjust emissions controls, but this must all be disclosed — and justified — during the COC process. If a vehicle contains undisclosed features that affect emissions, the COC would be considered invalid, notes the EPA.

Since this software was not disclosed during the COC process, the government contends that FCA violated federal law that prohibits the sale of new cars that aren’t covered by a COC.

That same law also makes it illegal to sell a car part whose principal purpose is to “bypass, defeat, or render inoperative any device or element of design installed in compliance” with the Clean Air Act; or to otherwise render such a device or design element inoperative.

The government is asking the court to grant an injunction barring FCA from selling vehicles with this undisclosed software, and to assess financial penalties against the carmaker.

In a statement, FCA says is reviewing the complaint but is “disappointed” by the government’s decision to file the suit. FCA denies that it “engaged in any deliberate scheme to install defeat devices to cheat U.S. emissions tests.”

The company says it has developed what it believes is a software fix for these vehicles that it hopes the EPA will approve.

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