DETROIT (AP) — The U.S. authorities’s auto security regulator has ended a 2 1/2-year investigation into Ford engine failures after the corporate changed engines or prolonged the guarantee on some autos.

The Nationwide Freeway Site visitors Security Administration says in paperwork posted Monday on its web site that its evaluation traced the issue to consumption valves that may fracture inside some 2.7-liter and 3-liter turbocharged engines.

Paperwork say the probe opened in Might of 2022 ended up overlaying greater than 411,000 autos from the 2021 and 2022 mannequin years together with the Ford F-150 Bronco, Edge and Explorer in addition to the Lincoln Aviator and Nautilus.

The company was wanting into catastrophic engine failures brought on by consumption valves fracturing, dropping into the cylinder and hitting the piston.

The paperwork say a forensic evaluation of fractured valves discovered that when the they had been made by a elements provider, the temperature received too excessive, making them brittle and prone to fracture throughout regular engine use.

An evaluation of failure report information discovered that the defective valves had been made out of Might by way of October of 2021, the company mentioned. Ford contended that not all valves produced throughout this era had been defective and {that a} overwhelming majority of the failures occurred earlier than the autos had been pushed 20,000 miles.

An company statistical evaluation to foretell the variety of failures, and an evaluation of failure studies “are typically constant” with Ford’s dedication that the valves would fail at low mileage, and nearly all of autos with the defective valves “have already skilled a failure,” the company mentioned.

Earlier this yr Ford recalled about 91,000 autos with valves made throughout the suspect interval. They’ll be examined and get a brand new engine if crucial. The corporate additionally prolonged the guarantee on autos with valves made throughout the interval to 10 years or 150,000 miles, the paperwork mentioned.

Throughout the investigation, the company mentioned it discovered 396 buyer complaints, 825 guarantee claims and 936 engine replacements. There have been no reported crashes or accidents.