By January 2016, the EPA began to voice frustration with FCA's "unacceptably slow pace" in attempting to explain high real-world NOx emissions.

Federal regulators apparently launched an investigation into Fiat Chrysler Automobiles diesel emissions just months after Volkswagen's TDI scandal first came to light.

Emails obtained by Jalopnik and Reuters via Freedom of Information Act requests suggest the Environmental Protection Agency reached out to FCA as early as November 2015. The agency had recently launched a screening program to determine if real-world emissions tests of vehicles from various automakers showed higher levels of nitrogen oxides than records based on static lab tests originally used for compliance certification.

"I am very concerned about the unacceptably slow pace of the efforts to understand the high NOx emissions we have observed," the EPA's director of vehicle compliance, Byron Bunker, wrote in a January 2016 e-mail to FCA North America's emissions compliance head, Vaughn Burns.

Bunker was direct in stating that some of FCA's diesel vehicles appeared to integrate auxiliary emissions control devices (AECD) that "to me ... violate EPA's defeat device regulations."

FCA's then-new head of vehicle safety and regulatory compliance, Michael Dahl, soon issued a separate email to the EPA calling for the agency to "reserve conclusions" until both sides can develop a "mutual understanding of the complex technical facts." The EPA appears to have taken a cautious approach at first, completing more testing and maintaining correspondence with FCA before ultimately pushing it into public view via a notice of violation in January 2017.

Both sides are now reportedly engaged in settlement negotiations, potentially exposing FCA to significant fines for more than 100,000 diesel vehicles sold in the US market.