NHTSA Engineering Analysis EA22001

On March 29, 2021, the Office of Defects Investigation (ODI) opened a Preliminary Evaluation (PE 21-009) after the agency received 58 reports alleging engine stalling in 2013-2016MY Audi vehicle models A8, S6, S7, S8 & RS7 equipped with the 4.0L, twin-turbocharged engine. Complainants reported the vehicles would stall with no warning while driving at highway or city traffic speeds. Several of the complainants alleged an inability to restart. The complaints alleged the major contributing factor to the engine stalling was the failure of the turbochargers. The complaints cited the turbocharger failure was a result of oil starvation due to a clogged oil strainer in the turbocharger oil supply line.The location of the oil strainer in the turbocharger oil supply line is in the inner valley of the engine. It is not easily accessible, making servicing the component difficult. The oil strainer removes particles and carbon deposits from the oil before lubricating the turbochargers. Over time, if the debris is not removed from the oil strainer, it becomes clogged and prevents oil from flowing to the turbochargers. This causes the turbine bushings to run dry and overheat resulting in turbine shaft failure due to thermal stress.On April 04, 2022, PE21-009 was upgraded to an Engineering Analysis (EA22-001) to further assess the scope, frequency, and potential safety related consequences of the alleged defect. Volkswagen filed recall 22V-178 to replace the 30?m mesh oil strainer with a 90?m mesh oil strainer in the subject vehicles. VW introduced the larger mesh oil strainer into production in March of 2017 effecting the 2017-2018MY vehicles.ODI reviewed information from VW for vehicles that had the larger mesh installed in production. The data received showed, since the new oil strainer size of 90?m went into production for the 2017-2018MY, there has not been any reported incidents of turbocharger failures due to oil starvation or other failures that could be related to the large