PARIS (Reuters) - A French judicial inquiry into Fiat Chrysler (FCA) FCHA.MI over suspected emissions-test cheating centers on whether the carmaker misled buyers of Fiat, Alfa Romeo, Jeep and Lancia cars about emissions levels, according to a letter seen by Reuters.

FILE PHOTO: A Fiat logo is seen at a car dealership in Vienna, Austria, May 30, 2017. REUTERS/Heinz-Peter Bader/File Photo

The letter, dated Oct. 17 and sent by the magistrate leading the investigation to people involved in the probe, also says French investigators suspect attempts were made to hinder the work of one of the investigators, an official whose job is to note breaches of France’s consumer laws.

FCA France said in an emailed statement it had always cooperated with authorities in any investigation and will continue doing so in future.

The carmaker said it could not comment on this specific inquiry because it did not have access to the file or its details, but remained confident the matter would be clarified in due course.

French prosecutors opened a formal investigation into Fiat Chrysler in March over allegations that the carmaker cheated in diesel emission tests.

The precise nature of that inquiry has been vague.

In the letter, the head of the investigation says the suspected emissions cheating dated back to as early as September 2009 and involved brands including Fiat, Alpha Romeo and Jeep, but did not say over which period.

The letter says investigators also suspect “obstruction of the work of an official tasked with registering breaches of the consumer code”.

FCA’s Milan-listed shares closed down 0.6 percent.

The inquiry into Fiat Chrysler came in the wake of Volkswagen's VOWG_p.DE diesel emissions-test cheating, exposed by U.S. regulators in 2015, which triggered dozens more investigations into possible test-rigging by other carmakers.

The VW scandal helped prompt a push by some lawmakers to ban diesel engines and eventually all combustion engines.

In May, the U.S. Justice Department sued Fiat Chrysler, accusing it of illegally using software that led to excess emissions in nearly 104,000 U.S. diesel vehicles sold since 2014. It also faces numerous lawsuits from owners of those vehicles.

The European Union has also launched legal action against Italy for failing to properly police allegations of emissions-test cheating by Fiat Chrysler, following the VW scandal.