(Bloomberg) -- General Motors Co. has agreed to resolve allegations that nearly 6 million of its pickups and sport-utility vehicles released more emissions than the company reported, reaching a deal with the Biden administration to retire 50 million metric tons of carbon credits to offset the pollution.

The move is the result of a US Environmental Protection Agency investigation targeting certain 2012-2018 model year GM vehicles. Testing by the agency and GM found the vehicles were emitting more than 10% higher carbon dioxide on average than originally claimed in the automaker’s compliance reports. 

GM also agreed to pay $145.8 million in penalties to resolve fuel-efficiency compliance issues stemming from the EPA’s probe, a US National Highway Traffic Safety Administration spokesperson said in a statement. The auto safety regulator oversees fuel economy rules while the EPA polices tailpipe pollution.

The extra emissions were discovered as part of mandatory testing meant to ensure vehicles on the road are complying with federal tailpipe standards. Automakers are required to test vehicles that have been on the road for one year and again at four years and submit those results to the EPA.

GM disclosed in a regulatory filing earlier this year that it was negotiating with the agencies over the matter. The company estimated $450 million in total costs tied to the issue, it said in the filing.

“GM has at all times complied with and adhered to all applicable laws and regulations in the certification and in-use testing of the vehicles in question,” the company said in a statement. “We believe this is the best course of action to swiftly resolve outstanding issues with the federal government regarding this matter.”

The affected vehicles include roughly 4.6 million full-size pickups and sport-utility vehicles and some 1.3 million mid-size SUVs, including Chevrolet Equinox, Tahoe and Silverado models, the EPA said in its statement.

The action is the latest example of the EPA slapping automakers with penalties for running afoul of regulations governing tailpipe emissions. It comes after the agency stepped-up testing of vehicles in use today in response to Volkswagen AG’s diesel-emissions cheating scandal roughly a decade ago.

EPA Administrator Michael Regan stressed that the in-use testing and oversight are essential to the integrity of the government’s tailpipe standards. 

“Our investigation has achieved accountability and upholds an important program that’s reducing air pollution and protecting communities across the country,” Regan said in his agency’s statement.

--With assistance from Keith Laing.

(Updates with NHTSA fine, details on agreement from third paragraph.)

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