Cummins Inc. has begun a formal review of its emissions certification and compliance process relating to diesel engines it supplies to Fiat Chrysler Automobiles for Ram pickups, the engine-maker has announced.

The review came after questions from the U.S. Environmental Protection Agency and California Air Resources Board about the new diesel engine that powers the 2019 Ram 2500 and 3500 trucks. This 6.7-liter turbo diesel makes up to 1,000 pound-feet of torque and up to 400 horsepower. Ram unveiled the truck at the Detroit auto show in Janaury.

The review is being conducted with external advisors "to ensure the certification process for Cummins pickup truck applications is consistent with its internal policies, engineering standards and applicable laws," according to a company statement.

Cummins has voluntarily disclosed the review to regulators and other agencies, and will cooperate with them to ensure a complete and thorough review and implement recommendations for improvement, according to Cummins.

The review hasn't affected sales of the Ram pickups, according to a statement from FCA.

"FCA appreciates the efforts Cummins is taking to conduct its review," according to the statement. "While the issues that are being discussed are between Cummins and other stakeholders, we will cooperate fully as necessary. FCA will advise customers if any action is required."