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All codes/P0171

P0171

System Too Lean (Bank 1)

Moderate severity

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

  • 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.

    high

    Typical part cost: $50-300

  • 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.

    medium

    Typical part cost: $100-300

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First things to check

  1. 1Check for vacuum leaks using a smoke machine or by spraying carb cleaner around vacuum lines and intake manifold.
  2. 2Inspect the MAF sensor for dirt or damage; clean if necessary.

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Tools you may need

Already have a compatible scanner? Use it. If not, a Bluetooth OBD2 adapter can help you confirm engine codes and check supported live sensor data before replacing parts.

Illustration of a Bluetooth OBD2 adapter, not a product photo

Basic checks

Veepeak OBDCheck BLE

A Bluetooth LE adapter for reading standard engine codes and supported live data.

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Illustration of a Bluetooth OBD2 adapter, not a product photo

Regular diagnostics

vgate iCar Pro BLE 4.0

A Bluetooth LE adapter with an automatic sleep feature for routine code and sensor checks.

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Illustration of a Bluetooth OBD2 adapter, not a product photo

Another option

OBDLink CX

A Bluetooth LE adapter to consider when comparing supported vehicles and diagnostic apps.

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Illustrations shown, not product photos. Check vehicle, phone and app compatibility before buying. These adapters do not guarantee access to ABS, airbags or manufacturer-specific systems. Clearing a code does not repair the fault and can reset emissions readiness monitors.

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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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