P0171P0174
P0171 and P0174 are generic OBD-II diagnostic trouble codes indicating that the engine is running lean on Bank 1 and Bank 2, respectively. A lean condition means the air-fuel mixture has too much air relative to fuel, which is detected when the engine management computer sees fuel trims outside its expected range. These codes are often accompanied by a lit check engine light and may appear together on V‑engine configurations.
Common causes include vacuum leaks in the intake system (such as cracked hoses, the PCV valve, or
Diagnostic steps typically begin with reading live data and freeze-frame information, inspecting intake vacuum lines, and
Note that Bank 1 and Bank 2 refer to the two sides of a multi-bank engine; some