Answer :
OA. An 'exhaust manifold leak' is the most likely cause of a 'Fuel System Lean' fault code, as it allows extra air to enter the combustion process which leads to an air-fuel mixture with a higher ratio of air to fuel than the optimal 14.7:1.
If a vehicle is showing a 'Fuel System Lean' fault code, it indicates that the mixture of air and fuel in the engine is too high in air content compared to the optimal ratio of 14.7:1. This is known as a lean condition, and this can be caused by various factors that may allow excess air into the combustion process or restrict fuel delivery.
From the options provided, an exhaust manifold leak (OA) can lead to a lean code because it allows additional air to enter the engine that is not accounted for by the oxygen sensors. This additional air can throw off the air/fuel ratio sensed by the vehicle's computer. When the computer detects the imbalance (a higher ratio of air to fuel), it will attempt to correct it by adding more fuel through the fuel injection system.
Other options listed, such as a clogged EGR passageway, a plugged catalytic converter, and a stuck-closed EVAP purge valve, are less likely to cause a lean condition. Instead, these issues often lead to different types of fault codes related to the respective components and emissions systems.
