This trouble code indicates that the air/fuel mixture in the engine's first bank of cylinders is too lean – meaning there's too much air and not enough fuel. Bank 1 typically refers to the side of the engine containing cylinder #1.
Several things can cause this:
* Mass Airflow Sensor (MAF) problems: A faulty MAF sensor can provide inaccurate readings, leading to a lean mixture.
* Vacuum leaks: Leaks in the intake manifold, vacuum hoses, or other parts of the intake system can draw in excess air, making the mixture lean.
* Fuel injectors: Clogged or malfunctioning fuel injectors can prevent sufficient fuel from reaching the cylinders.
* Fuel pump: A weak fuel pump might not deliver enough fuel pressure.
* Fuel pressure regulator: A faulty regulator could allow too much fuel to return to the tank.
* Oxygen sensor (O2 sensor): A faulty O2 sensor can provide incorrect feedback to the engine control module (ECM), leading to a lean condition. (Though less likely to be the *direct* cause of a P0171, a bad O2 sensor can prevent the system from correcting a lean condition.)
Troubleshooting steps usually involve:
1. Visual inspection: Check for any obvious vacuum leaks, loose hoses, or damaged wiring.
2. MAF sensor test/cleaning: Clean the MAF sensor with MAF sensor cleaner (following the instructions carefully) or replace if necessary.
3. Fuel pressure test: Check fuel pressure to ensure it's within specifications.
4. Fuel injector testing: This often requires specialized equipment.
5. Vacuum leak test: Use a smoke machine or other method to detect vacuum leaks.
It's crucial to diagnose the underlying cause, rather than just clearing the code. Ignoring the problem can lead to engine damage. A professional mechanic can properly diagnose and repair the issue.
