P0171
P0171 System Too Lean Bank 1
P0171 means the engine computer is adding more fuel than normal on bank 1 because it sees too much air or not enough fuel.
How urgent is P0171?
A lean condition can cause hesitation and misfires. Diagnose soon, especially if paired with misfire codes.
Common symptoms
- Check engine light
- Rough idle
- Hesitation
- Surging idle
- Poor fuel economy
Likely causes
- Vacuum leak
- Dirty or failing MAF sensor
- Low fuel pressure
- Exhaust leak before O2 sensor
- PCV leak
What to check before replacing parts
1
Review short and long fuel trims
2
Smoke-test intake
3
Inspect PCV hoses
4
Clean/test MAF sensor
5
Verify fuel pressure
Use the code with symptoms
A code points at the system, not always the failed part. Add your vehicle, mileage, symptoms, and whether the check engine light is steady or flashing so the AI diagnostic can narrow the next step.