General Motors engineers say quality inspectors spotted and fixed an assembly-process glitch weeks ago that caused a ’14 Chevrolet Cruze Clean Turbo Diesel to sputter and stall during testing by WardsAuto.

“We saw the issue early at the plant and fixed it,” says Gary Altman, chief engineer for the car.

The Cruze diesel is GM’s first U.S. car with the technology in more than three decades. And while the competitive landscape of today’s industry demands flawless new-product launches, a smooth rollout of the Cruze diesel is doubly important because GM’s last attempt at marketing the technology in America failed in part due to reliability issues.

Media previews of early build vehicles also regularly uncover blemishes, although problems typically are fit-and-finish or noise-and-vibration issues. Mechanical issues, such as the Cruze diesel engine failure, are less common.

WardsAuto first reported the Cruze diesel engine failure through its Twitter feed.

According to Altman, a pressurized intake duct on the Cruze’s 2.0L turbodiesel became disconnected from the engine’s throttle body, leading to the roadside breakdown of a pre-production model in suburban Detroit on May 23.

The $25,795 Cruze diesel carrying two journalists and a GM public-relations staffer sputtered leaving a stoplight on a predetermined drive route after about two hours of testing. It stalled several minutes later attempting a 3-point turnaround before restarting and limping to a nearby convenience store.

The engine radiated an unusual amount of heat, a small amount of smoke emitted from the rear of the engine bay and fumes entered the cabin. No warning lights blipped on before the failure.

GM’s quality team at the Cruze’s Lordstown, OH, assembly plant actually uncovered the problem two build sequences prior to the launch of regular production in mid-April, executives say. The auto maker retrained workers assembling the piece and double-checked the process by secretly planting a faulty engine on the manufacturing line.

“We sent a rabbit down the system to ensure they made the fix,” Altman says.

However, the units used for the media preview were assembled prior to uncovering the glitch, and GM never circled back to double-check that batch of cars.