Engine Stall - Turbo Failure

On March 29, 2021, the Office of Defects Investigation (ODI) opened 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. The subject vehicles are equipped with 4.0L, twin-turbocharged engine. Complainants reported that the vehicles stall suddenly with no warning while driving on the highway or in city traffic. Several of the complainants alleged an inability to restart. The complaints allege the major contributing factor to the engine stalling is the failure of the turbochargers. The complaints further allege the turbocharger failure is a result of oil starvation due to a clogged oil strainer. 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 regular service difficult. The oil strainer removes dirty particles and carbon deposits from the oil before flowing to lubricate the Turbochargers. Overtime if the debris are not removed from the oil strainer, it clogs the strainer and prevents free flow of oil to the turbochargers and makes the turbine bushings to run dry and overheat which causes the turbine shaft to break due to thermal stress. In VW's response to ODI's Information Request letter, VW provided approximately 611 warranty claims with unique VINs, 70 Field Reports and 45 Consumer complaints. These reports allege engine stalling due to turbocharger failure similar to the NHTSA reports described above. To date, NHTSA has received approximately 98 allegations of stall due to turbocharger failures. The total of 824 reports shown in the table above eliminates duplicate reports received by both ODI and the manufacturer. This Preliminary Evaluation is being upgraded to an Engineering Analysis (EA) to further assess the scope, frequency, and potential safety related consequences of the alleged defect of engine stalling due to turbocharger failure The ODI complaints cited above ca