The automaker “is unaware of any injuries or accidents associated with these complaints,” a spokesman, Eric Mayne, said by email. He added that Chrysler takes customer concerns seriously and that there was no indication that the function of airbags or seatbelt tension was compromised.

The Pacifica is designed so that its airbags remain operational even during a loss of power, he said.

That is a crucial safety matter. A faulty ignition switch that General Motors used in small cars caused the vehicles to switch off and rendered their airbags inoperable. The fault was linked to at least 124 deaths, most caused when crashes occurred and the airbags failed to deploy. G.M. eventually paid $900 million to settle a federal criminal investigation related to the faulty switches, set aside nearly $595 million to compensate victims of crashes, and recalled 2.6 million cars.

How Fiat Chrysler responds to complaints of possible defects is a sensitive matter. In 2015, the highway safety agency found that the automaker had failed to promptly notify vehicle owners of recalls and delayed initiating repairs of defective models in 23 recalls covering 11 million vehicles. The agency fined Fiat Chrysler $105 million.

In 2016, the actor Anton Yelchin was killed when his Jeep Grand Cherokee, made by Fiat Chrysler, rolled backward down his driveway and crushed him. The vehicle had been part of a recall related to its electronic gearshift, but had not been repaired when the accident occurred.

Both Mr. Cohen and Mr. Patel have left their Pacificas with their dealers and have declined to take the cars back until the stalling issue is cleared up. Mr. Cohen is driving a loaner vehicle. Mr. Patel, whose Pacifica had 308 miles on it when it shut down on the highway, is trying to get his dealer or Fiat Chrysler to buy back the minivan from him.

Mr. Cohen said he was particularly frustrated because he had been discussing the matter with Fiat Chrysler engineers and quality officials over the last several weeks via phone and email. On Oct. 22, he wrote to the company’s chief executive, Sergio Marchionne, to bring the issue to his attention.