WASHINGTON — Ford Motor Co said on Friday the U.S. Justice Department has opened a criminal investigation into the automaker's emissions certification process in the United States, the latest company to come under scrutiny by U.S. officials.

Ford voluntarily disclosed the issue to the U.S. Environmental Protection Agency and the California Air Resources Board in February and hired outside experts to investigate its vehicle fuel economy and testing procedures after employees raised concerns. Ford said at that time it did not know whether it would have to correct data provided to regulators or consumers.

Ford reiterated Friday in a regulatory filing the concern does not involve the use of defeat devices.

The automaker since last fall has been investigating concerns raised by employees that incorrect calculations were used to translate test results into the mileage and emissions data submitted to regulators.

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."

U.S. and California regulators have been cracking down on automakers for emissions cheating following revelations in 2015 that German automaker Volkswagen AG had used defeat devices to make models equipped with diesel engines appear to comply with emissions standards when they emitted far more pollution than allowed in real-world driving.

In January, Fiat Chrysler Automobiles NV agreed to an $800 million settlement to resolve claims by the U.S. Justice Department and the state of California that it used illegal software to produce false results on diesel-emissions tests. A Justice Department criminal investigation is pending.

U.S. regulators are also investigating Daimler AG for alleged excess emissions in Mercedes-Benz diesel vehicles, but the Justice Department and EPA have declined to comment on the status of the probe.

Daimler has declined to comment, but has previously acknowledged it faces investigations in Germany and the United States.