New York (CNN Business) The Department of Justice has opened a criminal investigation into Ford's emissions testing practices, the company said Friday.

Ford F The investigation centers on the testing proceduresused to certify the fuel economy and emissions standards of its vehicles. The company self-reported concerns about its emissions certification process to the Environmental Protection Agency and the California Air Resources Board in February after employees flagged concerns.

The company has also hired an independent third party to look into its testing process. Automakers generally do their own fuel economy testing based on strict criteria and mathematical formulas. They then report the results to the government.

The company has said the investigation into its emissions certification does not involve the use of "defeat devices" software that can be used to cheat emissions testing.

Ford said it is fully cooperating with the federal investigation but that it couldn't provide guidance on its outcome or how it will affect the company.

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