P0171
System Too Lean (Bank 1)
Your engine's computer has detected that the air-fuel mixture in the first bank of cylinders is too lean, meaning there's too much air or not enough fuel for proper combustion.
The powertrain control module (PCM) has detected that the engine is running too lean on Bank 1, meaning there is too much air or not enough fuel in the air/fuel mixture.
Common causes
- high
Vacuum Leaks
Leaks in vacuum hoses, intake manifold gaskets, PCV valve, or brake booster can allow unmetered air into the engine, causing a lean condition.
Typical part cost: $50-300
- medium
Faulty Mass Air Flow (MAF) Sensor
A dirty or failing MAF sensor can incorrectly report less air entering the engine than there actually is, leading the PCM to inject too little fuel.
Typical part cost: $100-300
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First things to check
- 1Check for vacuum leaks using a smoke machine or by spraying carb cleaner around vacuum lines and intake manifold.
- 2Inspect the MAF sensor for dirt or damage; clean if necessary.
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Related codes
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Frequently asked questions
What does 'Bank 1' mean?
Bank 1 refers to the side of the engine that contains cylinder #1. On V-type engines, this is usually one side, while on inline engines, there's only one bank, which is always Bank 1.
Can a P0171 code cause my car to fail emissions?
Yes, a lean condition means the engine isn't burning fuel efficiently, leading to higher emissions of certain pollutants, which will likely cause your vehicle to fail an emissions test.
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