What is the cause of the Buick P0171 fuel system too lean?

[OClaire]

Buick P0171 fuel system too lean indicates that the mixture inside the engine is too lean, which prevents it from meeting the required standards during combustion, resulting in limited power output from the vehicle's engine. Symptom: Fuel trim refers to the electronic control unit (ECU) controlling fuel delivery by increasing or decreasing the injector opening time to achieve the optimal air-fuel ratio (air to gasoline mass ratio of 14.7:1). A too rich air-fuel ratio means excessive fuel delivery, while a too lean air-fuel ratio means insufficient fuel delivery. Causes: These include air leaks after the mass air flow (MAF) sensor, PCV system leaks, exhaust leaks near or before the oxygen sensor, clogged fuel injectors or other fuel system faults, EGR system leaks, and a contaminated MAF sensor (causing the electronic control module to underestimate air flow).