P0171: System Too Lean (Bank 1)
P0171 means too much air (or not enough fuel). Try cleaning the MAF sensor first — it's the cheapest fix and works surprisingly often.
Severity: moderate · System: Powertrain · Safe to drive: usually, short-term. Fix within a few weeks — running lean can eventually damage the catalytic converter.
Symptoms
- Rough idle
- Hesitation
- Slight loss of power
- Higher fuel economy briefly
Common causes
- Vacuum leak
- Dirty mass airflow (MAF) sensor
- Weak fuel pump
- Clogged fuel filter
Fair repair prices
| MAF sensor cleaning | $15–$60 |
|---|---|
| MAF sensor replacement | $200–$400 |
| Vacuum leak repair | $100–$400 |
| Fuel pump replacement | $400–$900 |
Ranges are US market averages (parts and labor). If your shop's quote is above the high end, ask for a line-item breakdown or run it through the invoice checker.
Other codes
- P0300 — Random / Multiple Cylinder Misfire Detected
- P0301 — Cylinder 1 Misfire Detected
- P0420 — Catalyst System Efficiency Below Threshold (Bank 1)
- P0430 — Catalyst System Efficiency Below Threshold (Bank 2)
- P0174 — System Too Lean (Bank 2)
- P0442 — Evaporative Emission Control System Leak (Small)
- P0455 — Evaporative Emission Control System Leak (Large)
- P0128 — Coolant Temperature Below Thermostat Regulating Temperature