It seems the EPA has had its eye on Fiat Chrysler Automobiles and their EcoDiesel V6 for quite a while.
Jalopnik and Reuters obtained emails from the EPA via the Freedom of Information Act that revealed the government agency had suspicions about possible cheating at FCA back in November 2015 - almost two months after the EPA announced Volkswagen's cheating with its diesel engines.
In an email sent on January 7, 2016 to Vaughn Burns, FCA North America’s head of vehicle emissions, certification, and compliance, director of the EPA's Transportation and Air Quality compliance division Bryon Bunker expressed concerns about FCA's slow response to explaining why their EcoDiesel engine was producing excess nitrogen oxide (NOx) emissions.
“I am very concerned about the unacceptably slow pace of the efforts to understand the high NOx emissions we have observed from several [redacted] vehicles with the [redacted],” said Bunker in his email.
Bunker also noted at meeting with FCA back on November 25, 2015 that at one of the auxiliary emission control devices used possibly violated EPA regulations.
A few days later, FCA’s head of vehicle safety and regulatory compliance, Mike Dahl sent an email to Christopher Grundler, director of the EPA’s office of transportation and air quality saying that he wanted to discuss the issues brought up by the EPA. Dahl noted that the company was hard at work investigating the issue.
There is also this tidbit from Dahl's email.
As I am sure you can appreciate, conclusions regarding possible noncompliance of FCA’s engine design, as violating EPA’s “defeat device” regulations, are conclusions of a legal nature with potentially significant regulatory and commercial consequences. We believe the best course is for both FCA and your team to reserve conclusions on that question until we both are comfortable that we fully and fairly have a mutual understanding of the complex technical facts of our emissions control strategy, of FCA’s rationale for the strategies, and a full and complete mutual understanding of your views. At that point, FCA is committed to cooperating with you to address any issues in an appropriate manner.
The emails between the EPA and FCA go back and forth throughout 2016 talking about the possible violations and additional testing. Jalopnik notes that the EPA was planning to make an announcement in December, but it is unclear whether it was to deal with the violation.