OBD2 Codes

P0174 – System Too Lean (Bank 2)

Mirror to P0171 on bank 2; usually shares the same root cause.

Details

Often appears with P0171. Focus on shared leaks and air metering issues before chasing bank-specific hardware.

Typical causesFord GM Toyota when upper plenum gaskets leak
SymptomsMIL on lean trims on bank 2 may be idle-specific
SeverityMedium — fix promptly to keep cats healthy
DIY checksSolve P0171 root causes first then recheck trims on both banks
ToolsFuel trim targets: STFT/LTFT ideally within ±5% above +10% indicates lean

Utilities

Copy-paste helpers

Quick checklist

Solve P0171 root causes first then recheck trims on both banks

Related

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P0171 – System Too Lean (Bank 1)

Air/fuel mixture too lean on bank 1; commonly vacuum leaks or a dirty MAF

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FAQ

Common questions

Can a clogged air filter cause lean codes?

Yes—restriction skews MAF readings and can trigger lean conditions.

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