P0171
Medium SeveritySystem Too Lean (Bank 1)
Fuel System
What Does P0171 Mean?
The engine is running lean on bank 1 — too much air or not enough fuel. The ECM has maxed out its fuel trim trying to compensate. Common causes include vacuum leaks and dirty MAF sensors.
Common Fix
Fix vacuum leak or clean MAF sensor
Estimated Cost (DIY)
$0 - $150
Symptoms
- ⚠️Rough idle
- ⚠️Hesitation on acceleration
- ⚠️Poor fuel economy
- ⚠️Possible misfire at idle
Common Causes
Vacuum leak (intake manifold gasket, hose, PCV)likely
Dirty or failed MAF sensorlikely
Weak fuel pump or clogged filterpossible
Leaking fuel injectorpossible
How to Diagnose P0171
- 1Check for vacuum leaks with smoke test or carb cleaner
- 2Clean MAF sensor with MAF cleaner
- 3Check fuel pressure
- 4Inspect intake manifold gaskets
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Frequently Asked Questions
- Can I drive with P0171?
- You can drive but the engine runs lean, which causes poor performance and can damage the catalytic converter over time.
- What is the most common cause of P0171?
- A vacuum leak (cracked hose, loose clamp, or leaking intake gasket) is the #1 cause, followed by a dirty MAF sensor.