Engine code P0171 means that an oxygen sensor in a vehicle’s engine has detected too much oxygen in the exhaust. It is often caused by intake air leaks, faulty fuel injectors and exhaust gas leaks.
Code P0171 is one of the more common trouble codes. An internal oxygen sensor triggers this code when it senses too much air in the system. The sensor provides a reading of the air/fuel ratio leaving the engine's cylinders.The vehicle's powertrain/engine control module uses that reading and adjusts to keep the engine running at that optimum ratio. If the ratio cannot be maintained and there is too much air, it triggers this code.