P0171 — System Too Lean (Bank 1)
Drive with caution — fix soon.
What P0171 means
P0171 means the engine is running too lean on bank 1, meaning the air-fuel mixture has too much air or not enough fuel. The computer noticed it's adding extra fuel to compensate but still can't reach the right balance. On most engines bank 1 is the side that contains cylinder 1.
Common symptoms
- Check engine light on
- Rough or unstable idle
- Hesitation or lack of power
- Occasional misfire or surging
- Possible hard starting
Common causes
- Vacuum or intake air leak
- Dirty or faulty mass airflow (MAF) sensor
- Weak fuel pump or clogged fuel filter
- Clogged fuel injectors
- Leaking or worn PCV system
- Faulty oxygen sensor
Typical repair cost
$100 – $550
Varies by vehicle and root cause.
Frequently asked questions
Can I drive with P0171?
Usually yes, for the short term, but don't let it linger. A lean condition can lead to misfires and added heat, so have it checked soon.
How much does it cost to fix a P0171?
It varies with the cause: cleaning a MAF sensor or fixing a vacuum leak can be $100-$250, while a fuel pump or injector job can run $300-$550 or more.
Is a P0171 serious?
It's moderate. It won't usually strand you right away, but a long-term lean mixture can cause misfires and engine wear, so it shouldn't be ignored.
What's the most common cause of P0171?
Unmetered air getting into the engine is the most frequent cause, typically from a vacuum leak or a dirty mass airflow sensor.