General Motors is postponing the launch of a new inline-six turbodiesel engine in the Chevrolet Silverado 1500 and GMC Sierra 1500 until the 2020 model year, according to Automotive News.

The EPA’s emissions certification process for the engine is taking longer than anticipated, creating a “slight delay,” according to a memo GM sent to dealers Tuesday. The full-size diesel pickups were expected to go on sale for the 2019 model year in early 2019, months after gasoline versions started arriving at dealerships last fall.

GM said 2020 diesel pickup production will begin “soon” but the delay means dealer orders for the models will be canceled and must be resubmitted.

Dealers and customers impacted by the cancellation will be offered a replacement 2020 vehicle, according to the memo.

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