Quick checklist
Solve P0171 root causes first then recheck trims on both banks
OBD2 Codes
P0174 – System Too Lean (Bank 2)
Mirror to P0171 on bank 2; usually shares the same root cause.
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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
Related
Other pages in OBD2 Codes
FAQ
Common questions
Can a clogged air filter cause lean codes?
Yes—restriction skews MAF readings and can trigger lean conditions.