A vehicle displaying a P0171 trouble code and failing for high HC emissions likely indicates what issue?

A vehicle that displays a P0171 trouble code typically points to a lean condition in the engine, which means there is not enough fuel being mixed with the incoming air. This lean condition can lead to high hydrocarbon (HC) emissions as the vehicle struggles to maintain proper combustion efficiency.

When considering the possibilities, a leaking intake manifold gasket is a common cause of such an issue. A leak in the intake manifold gasket allows excess air to enter the engine, disrupting the optimal air-fuel mixture. This results in an imbalanced mixture, often leading to high HC emissions due to incomplete combustion, as not enough fuel is present to burn completely.

While other potential issues, like faulty mass air flow sensors or defective oxygen sensors, can also affect the air-fuel mixture, they typically present different symptoms or trouble codes. A leaking fuel injector could introduce too much fuel rather than causing a lean condition, which is why it’s less likely to be the issue at hand when considering the P0171 code.