System Too Lean (Bank 1)
What it means
The engine is running with too much air relative to fuel on bank 1; the ECU has hit its correction limit trying to add fuel.
Symptoms
Rough idle, hesitation, lack of power, sometimes a check-engine light only.
Common causes
Vacuum/intake leak, dirty MAF sensor, weak fuel pump, clogged injectors, or a leaking PCV.
Recommended action
Check for intake leaks and clean/inspect the MAF sensor first — these are the usual culprits.
Related codes
FAQ — P0171
What does code P0171 mean?
System Too Lean (Bank 1). The engine is running with too much air relative to fuel on bank 1; the ECU has hit its correction limit trying to add fuel.
What are the symptoms of P0171?
Rough idle, hesitation, lack of power, sometimes a check-engine light only.
What causes P0171?
Vacuum/intake leak, dirty MAF sensor, weak fuel pump, clogged injectors, or a leaking PCV.
What should I do about P0171?
Check for intake leaks and clean/inspect the MAF sensor first — these are the usual culprits.
General reference based on the SAE J2012 standard. Exact causes for your vehicle may differ — when in doubt, consult a workshop.
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