GM has been accused in a lawsuit of rigging hundreds of thousands of diesel trucks with devices similar to those used by Volkswagen to ensure they pass emissions tests.
General Motors is being sued for allegedly rigging diesel engine versions of its Silverado and Sierra HD vehicles to pass emissions tests.
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The proposed class-action lawsuit covers people who own or lease more than 705,000 Chevrolet Silverado and GMC Sierra pickups fitted with "Duramax" engines from the 2011 to 2016 model years.
It said GM used at least three "defeat devices" to ensure that the trucks met federal and state emission standards, even if they generated more pollution in real-world driving. The complaint was filed in the federal court in Detroit.
"These claims are baseless and we will vigorously defend ourselves," GM spokesman Dan Flores told Reuters.
He also told the news agency that the trucks comply with U.S. Environmental Protection Agency emissions standards and California's own tough emissions standards.
GM joins VW, which has admitted to cheating, and at least four other automakers – including Daimler, FCA, PSA and Renault – whose diesel emissions have been questioned.
Reports of the lawsuit say it suggests "on-road" emissions testing conducted for the plaintiffs found that Duramax-engined trucks produced nitrogen oxide pollutants two to five times higher than allowed.
Tie 1 supplier Bosch was also named as a defendant for having allegedly helped develop the defeat devices.
