P0171

System Too Lean (Bank 1)

Q: What does fault code P0171 mean?

System Too Lean (Bank 1). ECM is adding maximum fuel and O2 sensors still report lean on bank 1. Unmetered air or insufficient fuel delivery.

Q: What are the symptoms of P0171?

CEL; Rough idle; Hesitation; Possible whistle from vacuum leak

Q: What are the possible causes of P0171?

Vacuum leak (intake, PCV, booster); Dirty/failing MAF; Weak fuel pump or clogged filter; Clogged injectors; Faulty O2; Exhaust leak before upstream O2

Q: How to fix P0171?

Inspect vacuum lines and intake boots; Clean MAF; Check fuel pressure; Smoke-test intake; Monitor STFT/LTFT

Severity: Medium Fuel & Air Metering Generic OBD-II Code Est. Repair: $100 - $500

Schedule diagnosis soon. Continued driving may worsen the issue.

What Does P0171 Mean?

ECM is adding maximum fuel and O2 sensors still report lean on bank 1. Unmetered air or insufficient fuel delivery.

Common Symptoms

CEL

Rough idle

Hesitation

Possible whistle from vacuum leak

Possible Causes

Vacuum leak (intake, PCV, booster)

Dirty/failing MAF

Weak fuel pump or clogged filter

Clogged injectors

Faulty O2

Exhaust leak before upstream O2

How to Fix P0171 – Repair Guide

Inspect vacuum lines and intake boots

Clean MAF

Check fuel pressure

Smoke-test intake

Monitor STFT/LTFT

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Disclaimer: Information is for educational reference only and does not replace professional diagnosis. Actual causes and costs vary by vehicle make, model, year and condition. Always verify with a qualified technician.