OBD-II · P0171
P0171 Code: System Too Lean (Bank 1) — Causes & Fixes
System too lean (Bank 1)
The short version
Short-term driving is usually okay, but a chronic lean condition can cause hesitation and extra engine heat over time, so don't delay diagnosis for long.
- Severity: Moderate
- Most common cause: Vacuum hose or intake gasket leak
- 6 diagnosis steps in order
- 5 symptoms tied to this code
Darker bars are the more common causes; bar length is the top expected repair cost. Start with the dark, cheap causes before the expensive ones.
Can I keep driving?
Short-term driving is usually okay, but a chronic lean condition can cause hesitation and extra engine heat over time, so don't delay diagnosis for long.
Symptoms
- Rough idle or slight hesitation
- Mild loss of acceleration
- Increased fuel consumption
- Occasional hissing sound near the intake (vacuum leak)
- Check engine light with other lean-related codes
Causes & repair cost
Vacuum hose or intake gasket leak
Most common$80 – $350
Dirty or failing mass airflow (MAF) sensor
Most common$20 – $250
Clogged air filter or loose air intake components
Possible$20 – $60
Dirty fuel injectors or weak fuel pump
Possible$150 – $600
Intake manifold gasket leak
Rare$200 – $550
Cheap fixes (a loose hose, dirty air filter) can cost almost nothing, while a MAF sensor or intake gasket job runs higher — final cost always depends on the specific vehicle and shop labor rates.
Estimate the repair for your carDiagnosis steps in order
- Inspect the air filter condition
- Search for vacuum leaks with smoke test or spray method
- Clean the MAF sensor and check live data readings
- Test fuel pressure and pump output
- Visually inspect intake manifold gaskets
- Clear the code and re-test to confirm the fix
FAQ
Can I drive with a P0171 code?
Short trips are fine, but get it checked soon to avoid rough running developing further.
What's the difference between P0171 and P0174?
P0171 is for Bank 1 and P0174 is for Bank 2 on V6/V8 engines with two banks.
Does cleaning the MAF sensor fix P0171?
Sometimes, if a dirty sensor was the only cause — but not always.
Is a vacuum leak dangerous?
Not immediately dangerous, but it hurts performance and fuel economy over time.
Related codes
All explained codes
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