MILAN (Reuters) - Any potential fines Fiat Chrysler (FCA) may need to pay to settle a U.S. civil lawsuit over diesel emissions will unlikely top $1 billion, analysts said, adding the case appeared less serious than at larger rival Volkswagen VOWG_p.DE.

A woman walks past a logo of Fiat Chrysler Automobiles (FCA) in Turin March 31, 2014. REUTERS/Giorgio Perottino

The U.S. government filed a civil lawsuit on Tuesday accusing FCA of illegally using software to bypass emission controls in 104,000 vehicles sold since 2014, which it said led to higher than allowable levels of nitrogen oxide (NOx) that are blamed for respiratory illnesses.

FCA’s shares dropped 16 percent in January when the U.S. Environmental Protection Agency (EPA) first raised the accusations, adding the carmaker could face a maximum fine of about $4.6 billion. The stock has been under pressure since.

Volkswagen agreed to spend up to $25 billion in the United States to address claims from owners, environmental regulators, U.S. states and dealers. FCA, which sits on net debt of 5.1 billion euros ($5.70 billion), lacks VW’s cash pile but analysts said its case looked much less severe.

While VW admitted to intentionally cheating, Fiat Chrysler denies any wrongdoing. Authorities will have to prove that FCA’s software constitutes a so-called “defeat device” and that it was fitted in the vehicles purposefully to bypass emission controls.

Even if found guilty, the number of FCA vehicles targeted by the lawsuit is less than a fifth of those in the VW case.

Applying calculations used in the German settlement, analysts estimate potential civil and criminal charges for Fiat Chrysler of around $800 million at most. Barclays has already cut its target price on the stock to take such a figure into account.

Analysts also noted that FCA’s vehicles are equipped with selective catalytic reduction (SCR) systems for cutting NOx emissions, so it is likely that any problem could be fixed through a software update.

“Should this be the case, we estimate a total cost per vehicle of not more than around $100, i.e. around $10 million in aggregate,” Evercore ISI analyst George Galliers said in a note.

The estimates exclude any additional investments FCA may be asked to make in zero emissions vehicles infrastructure and awareness as was the case with VW.

FCA said last week it would update the software in the vehicles in question, hoping it would alleviate the regulators’ concern, but analysts said it may have been too little too late.

The carmaker is also facing accusations over its diesel emissions in Europe.

Investors remain wary over what any potential penalties will mean for FCA’s 2018 targets, including its promise to erase debt.

If necessary, the carmaker could consider selling some of its assets, including parts maker Magneti Marelli or luxury brand Maserati. FCA has so far excluded the need for any disposals to reach the 2018 goals.

“If FCA is required to make a substantial payment, we believe all options will be visited,” Galliers added.