P0171 Code: System Too Lean (Bank 1)
🟠 Moderate severity · drivable
Drivable short-term, but a lean condition can cause misfires and, over time, engine damage, so don't ignore it.
What P0171 means
The engine is running lean on bank 1 — that means too much air or not enough fuel in the combustion mixture. The engine computer has tried to add fuel to correct it and hit its limit, so it sets P0171.
Symptoms
- Check engine light is on
- Rough or surging idle
- Hesitation or lack of power under acceleration
- Poor fuel economy
- Possible stalling
Common causes
- most common: Vacuum leak (cracked hose or leaking intake gasket)
- common: Dirty or failing mass air flow (MAF) sensor
- common: Weak fuel pump or clogged fuel filter
- less common: Faulty upstream oxygen sensor
- less common: Leaking fuel injector or intake manifold gasket
How to fix it
| Fix | DIY? | Typical cost |
|---|---|---|
| Inspect and repair vacuum leaks (hoses, intake boot, gaskets) | Yes | $10–100 |
| Clean the mass air flow sensor with MAF cleaner spray | Yes | $10–20 |
| Replace the upstream oxygen sensor if it's reading incorrectly | Yes | $60–200 |
| Replace a weak fuel pump or clogged fuel filter | Mechanic | $300–800 |
Frequently asked questions
Can I drive with a P0171 code?
Yes for a short time, but a lean engine runs hotter and can misfire. Fix it soon to avoid damaging the catalytic converter or engine.
What is the most common cause of P0171?
A vacuum leak is the most common cause — unmetered air getting into the engine after the mass air flow sensor. A dirty MAF sensor is a close second.
Is P0171 expensive to fix?
Often not. Vacuum hose and MAF cleaning fixes cost $10–$100. It only gets expensive if the fuel pump or a major gasket is the cause.
Related codes
P0174
P0174 Code: System Too Lean (Bank 2)
P0101P0101 Code: Mass or Volume Air Flow (MAF) Sensor Circuit Range/Performance
P0300P0300 Code: Random/Multiple Cylinder Misfire Detected
Updated 2026-08. This page is informational and not a substitute for professional diagnosis.