Fiat Chrysler Automobiles continues to be dogged by allegations that it cheated on various diesel-emissions tests.

In the U.S., the company faces two lawsuits alleging that diesel vehicles use "defeat device" software to circumvent emissions tests in a similar manner to Volkswagen's cheating TDI vehicles.

In January, the EPA said FCA had failed to disclose eight software routines in its EcoDiesel 3.0-liter V-6 that affect emissions, but did not confirm whether these pieces of software constituted illegal "defeat devices."

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Now French prosecutors are investigating the Italian-American automaker for what they call "aggravated cheating" on diesel emissions, according to Reuters.

An anonymous judicial source told the news service that the investigation was opened March 15, after France's consumer-affairs agency referred the matter to the courts.

While U.S. lawsuits allege FCA's large diesel pickup trucks and SUVs produced excess emissions, European on-road emissions tests have indicated the automaker's passenger cars may be producing illegally high levels of emissions.

2017 Fiat 500S

In the wake of the Volkswagen diesel scandal, France began to conduct on-road emissions tests to confirm that new vehicles complied in real-world use with pollution standards, as current laboratory tests indicate they do.

On-road tests are more realistic and less easy to cheat, but are also time consuming and costly, which is why laboratory tests are currently the standard procedure in virtually all countries.

ALSO SEE: Every diesel brand in Europe emits more than VW, says new report (Sep 2016)

Results from France's tests have reportedly led to four automakers being targeted by prosecutors.

They include not only Fiat Chrysler, but also Volkswagen, Renault, and PSA Peugeot Citroën. The German Opel unit of General Motors was not included among those targeted.

2017 Fiat 500L

Testing by environmental group Transport & Environment last year pegged Fiat as one of the worst offenders when it came to excess emissions.

T&E found that no automaker selling cars in Europe met current emissions standards, but that certain Fiat diesel models averaged 15 times the legal limit of nitrogen-oxide emissions in real-world use.

CHECK OUT: French target Renault, Brits query Fiat, over diesel emissions

France's investigation follows inquiries made by British authorities into FCA diesel-emissions cheating in January.

The U.K. Department of Transportation asked the EPA for information about its allegations against the automaker at that time.

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