The company already faces accusations in Europe that its cars produce far more nitrogen oxides in normal driving than during tests. On Wednesday, the European Union’s executive arm filed a formal complaint against the Italian government for allowing Fiat Chrysler to sell cars designed to evade emissions tests.
And the evidence has piled up that those high emissions levels were part of efforts to evade environmental standards.
Academic researchers on both sides of the Atlantic said separately this week that they had found that Fiat Chrysler’s diesel vehicles had suspiciously high pollution levels and that there was evidence the company had used a so-called defeat device, software intended to allow a vehicle to pass official emissions tests but to pollute more when driven on the highway.
In the latest instance, the American university researcher who exposed Volkswagen’s emissions scandal said in a telephone interview late Thursday that tests of Jeep Grand Cherokees and Ram 1500 had revealed major discrepancies between road and lab emissions.
Dan Carder, director of a renowned vehicle emissions program at West Virginia University, said a diesel Ram pickup tested by the group produced up to 20 times as much harmful nitrogen oxides on the road than under controlled conditions in a lab. A diesel Jeep Grand Cherokee produced up to five times as much.
A 2013 study by Mr. Carder’s team set off a chain of events that exposed Volkswagen’s use of illegal software to conceal excess emissions in diesel cars. That led to Mr. Carder being named one of Time magazine’s 100 most influential people last year. Eventually the German automaker paid more than $22 billion in legal settlements and fines stemming from the cheating.
Mr. Carder said he did not try to determine whether the Fiat Chrysler vehicles were equipped with so-called defeat devices, but said that such big discrepancies between lab and road tests were unusual.
“It suggests different emission control versus what’s in the laboratory,” he said.
While it is normal for diesel vehicles to pollute somewhat more in normal driving than in the controlled environment of a lab, Mr. Carder said, “when you get to five times that’s kind of eye raising.”
While he stopped short of accusing Fiat Chrysler of using illegal software, a separate study found evidence that the company had done so.