General Motors will start shipping diesel versions of its full-sized pickups after a three month delay due to emissions certification.

Reports indicate the automaker had intended to begin shipping diesel versions of its Chevy Silverado and GMC Sierra in May. However, the Environmental Protection Agency (EPA)’s certification process for diesel engines took longer than expected. BMW, Fiat Chrysler and others have previously delayed vehicle releases due to certification issues.

The new Silverado and Sierra will be marketed as 2020 models. They feature 3.0-liter turbodiesel engines, the first time GM has put such an engine in a light duty pickup since 1997. The engines are built at GM’s facility in Flint, Mich.