WASHINGTON/DETROIT (Reuters) - Cummins Inc has agreed to recall about 500,000 medium- and heavy-duty trucks in the United States to correct a faulty emissions control system in the engines it made for the trucks, the U.S. Environmental Protection Agency said on Tuesday.

Flags fly outside the U.S. Environmental Protection Agency (EPA) at EPA headquarters in Washington, U.S., July 11, 2018. REUTERS/Ting Shen

The EPA said the Cummins recall of vehicles produced between 2010 and 2015 was the largest ever voluntary recall of trucks due to emissions problems. The catalytic reduction systems were found to be less durable than required and will be replaced, it said.

A spokesman for Cummins said the recall was “in the best interests of our customer and the environment.”

The recall is to replace a faulty emissions control systems component that causes excess nitrogen oxides (NOx) emissions. The problem is the result of a defective part and was discovered during emissions standards compliance tests by the California Air Resources Board, which said Cummins “worked collaboratively” with the regulator on the recall.

The Cummins spokesman said the recall will be rolled out in two phases, starting with heavy-duty trucks in August and medium-duty trucks next March.

A previous recall that is underway involves Cummins engines in around 232,000 Dodge Ram 2500 and 3500 pickup trucks made by Fiat Chrysler Automobiles NV.

The EPA said the problem does not involve illegal software known as “defeat devices,” which increase the effectiveness of emissions filters to mask pollution levels during tests.

Volkswagen AG VOWG_p.DE has been found guilty of using such software to pass U.S. emissions tests in the "dieselgate" scandal which came to light in 2015.

Audi AG’s Chief Executive Rupert Stadler was suspended after his arrest in mid-June as part of a broader probe into emissions cheating at the premium brand, which is part of the VW group.

Stadler has appealed to a court to be released from custody.