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P0171 System Too Lean (Bank 1)
What it means
The engine computer is adding a lot of extra fuel on bank 1 to make up for too much air or too little fuel. The mixture is running lean.
Severity: Moderate
Can I drive it? Usually drivable short-term, but lean running can cause misfires, hesitation, and eventual engine or converter damage.
Common causes (most likely first)
- Vacuum leak (cracked hose, intake gasket, PCV hose)
- Dirty or faulty MAF sensor
- Weak fuel pump / clogged fuel filter / low fuel pressure
- Clogged or leaking fuel injectors
- Exhaust leak before the upstream O2 sensor
Likely fixes
- Inspect and smoke-test for vacuum leaks
- Clean the MAF sensor
- Test fuel pressure
- Replace faulty hoses/gaskets
DIY parts cost
$10–$250
Approximate estimate
Shop repair cost
$100–$800
Approximate estimate, parts + labor
DIY difficulty
Easy to Moderate
Varies by vehicle
Cost ranges are rough, approximate U.S. estimates and vary widely by vehicle, region, and parts brand. Always confirm the diagnosis before buying parts.
Parts you may need
- MAF sensor cleanerCheck price
- Vacuum hoseCheck price
- PCV valveCheck price
- Intake manifold gasketCheck price
- Fuel filterCheck price
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