However, Ford said the concerns did not involve the use of defeat devices - the cheat software used to deliberately lower emissions during official tests, which were at the heart of the Volkswagen "dieselgate" scandal in 2015.
Ford is the latest automaker tangled up in allegations of emissions testing misconduct.
Ford could be the next auto maker to be caught up in the emissions scandals that have rocked the industry since Volkswagen's admission in 2015 that it cheated pollution tests.
Ford said in February it was evaluating changes to the process it uses to develop fuel economy and emissions figures, "including engineering, technical and governance components".
Ford made the disclosure in an SEC filing Friday.
When Fiat Chrysler agreed to settle a dispute involving its own Jeep and Ram diesel models this past January it was socked with an $800 million bill for both civil penalties and payouts to vehicle owners. The Justice Department stepped in afterward, according to the regulatory filing.
Ford said it had been looking into concerns raised by employees since last fall that incorrect calculations were used to translate test results into vehicle mileage and emissions data submitted to regulators.
The EPA's listing for the 2019 Ford Ranger at fueleconomy.gov includes a curious third entry for a truck with only two variants that affect gas mileage. It could wind up having to reverse itself, for one thing, after having declared that its new Ranger pickup had the highest fuel economy of any gas-powered midsize pickup truck available in the US market. That prompted Ford to then hire a company to help conduct a review, and also to notify regulators including the Environmental Protection Agency.
Earlier this month, German prosecutors charged Volkswagen chief executive Martin Winterkorn and four other managers of fraud.
The company also said it can not predict the outcome of the investigation and "cannot provide assurance that it will not have a material adverse effect on us".