This indicates that the air/fuel mixture in the engine's cylinders on Bank 1 (usually the side of the engine containing cylinder #1) is too lean – meaning there's too much air and not enough fuel. This can be caused by a variety of issues, including:
* Mass Airflow Sensor (MAF) problems: A faulty MAF sensor can provide incorrect readings to the computer, leading to a lean mixture.
* Vacuum leaks: Leaks in the intake system allow excess air to enter, upsetting the air/fuel ratio.
* Fuel injector problems: A clogged or malfunctioning fuel injector on Bank 1 can prevent sufficient fuel from being delivered.
* Fuel pump issues: A weak fuel pump may not supply enough fuel pressure.
* Fuel filter clog: A clogged fuel filter restricts fuel flow.
* EGR valve problems: A malfunctioning EGR valve can cause a lean condition in some cases.
* Oxygen sensor problems: While less likely to be the primary cause of a P0171 code, a faulty oxygen sensor can contribute to the problem by providing inaccurate feedback to the engine control unit (ECU).
To diagnose the issue, a mechanic will typically perform a series of tests, including checking the MAF sensor, inspecting for vacuum leaks, testing fuel pressure, and examining the fuel injectors and oxygen sensors. Simply clearing the code won't fix the underlying problem. It's crucial to address the root cause to prevent further engine damage.
