The move came a day after the company said it was in talks to resolve a Justice Department investigation. The case bears striking similarities to a Volkswagen scandal in which several executives have been investigated or charged, with the German carmaker paying tens of billions of dollars in fines, penalties and settlements.
Though Fiat Chrysler is unlikely to have to pay as much as Volkswagen, the emissions cheating, if proved, could still be expensive and badly damage the company’s reputation at a time when it is grappling with low profitability.
On Friday, Fiat Chrysler said it was modifying Jeep Grand Cherokees and Ram 1500 diesel vehicles in the 2014 through 2016 model years with “updated emissions software calibrations.” It said it was also seeking regulatory approval for 2017 models with the same software.
The carmaker said the move was the “result of many months of close collaboration” with the Environmental Protection Agency and the California Air Resources Board. Fiat Chrysler said it thought the updates would help it reach settlements with the E.P.A. and the Justice Department.
The Justice Department has been investigating Fiat Chrysler since the E.P.A. in January accused the carmaker of violating clean-air rules. Fiat Chrysler said this week that it was trying to work out a settlement with the Justice Department, but added that it would fight any suggestion that it had used illegal software to dupe regulators.
In 2015 and 2016, the company sold more than 50,000 diesel Ram pickups in the United States each year, making the model the country’s largest-selling diesel-powered light vehicle by far, according to HybridCars.com. But the emissions question has kept Fiat Chrysler from selling any diesel Ram or Grand Cherokee vehicles this year because the E.P.A. has not certified them for sale.
The E.P.A. declined to comment about Fiat Chrysler’s announcement.