This code indicates that the powertrain control module (PCM) has detected a lean air/fuel mixture in bank 1 of the engine. Bank 1 typically refers to the side of the engine that contains cylinder #1. A lean mixture means there's too much air and not enough fuel being delivered to the engine.
Several things can cause this:
* Vacuum Leaks: A leak in the intake manifold, vacuum hoses, or other parts of the intake system can introduce excess air, leading to a lean condition. This is a very common cause of P0171.
* Mass Airflow Sensor (MAF) Issues: A faulty MAF sensor might be providing inaccurate readings to the PCM, leading to incorrect fuel delivery. A dirty MAF sensor can also cause this.
* Fuel Injectors: Clogged or malfunctioning fuel injectors can prevent the proper amount of fuel from being sprayed into the combustion chamber.
* Fuel Pump: A weak fuel pump might not be delivering enough fuel pressure.
* Fuel Pressure Regulator: A faulty fuel pressure regulator might not maintain the correct fuel pressure.
* Oxygen Sensor (O2 Sensor): A faulty O2 sensor (especially the upstream sensor on Bank 1) can provide incorrect feedback to the PCM, causing it to adjust the fuel mixture incorrectly.
* EGR Valve: Problems with the exhaust gas recirculation (EGR) system can sometimes contribute to lean conditions.
Important Note: Simply clearing the code won't fix the problem. You need to diagnose the underlying cause using a multimeter, a vacuum gauge, and potentially a scan tool to check live data from various sensors. It's best to take the vehicle to a qualified mechanic for proper diagnosis and repair.
