P0174
System Too Lean (Bank 2)
Your engine's computer has detected that the air-fuel mixture in the second bank of cylinders (if your engine has two) 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 2, meaning there is too much air or not enough fuel in the air/fuel mixture.
Common causes
- high
Vacuum Leaks
Leaks in vacuum lines, intake manifold gaskets, or PCV system can allow unmetered air into the engine, causing a lean condition, especially if localized to Bank 2.
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 for both banks.
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, focusing on Bank 2 side.
- 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 2' mean?
Bank 2 refers to the side of the engine that does NOT contain cylinder #1. This code only applies to V-type or Boxer engines that have two separate exhaust banks.
If I have both P0171 and P0174, what's the likely cause?
If both codes appear, it strongly suggests a problem affecting both banks equally, such as a large vacuum leak common to both sides (e.g., intake manifold gasket), a faulty Mass Air Flow (MAF) sensor, or a general fuel delivery issue like a weak fuel pump or clogged fuel filter.
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