P0171Medium severity
System Too Lean (Bank 1)
The air-fuel ratio on bank 1 is too lean — there is too much air or not enough fuel — beyond what fuel trims can correct.
Common causes
- Vacuum or intake air leak
- Dirty MAF sensor
- Weak fuel pump or clogged fuel filter
- Faulty oxygen sensor
Possible symptoms
- Check Engine Light on
- Rough idle
- Hesitation
- Loss of power
Code breakdown
P — System
Powertrain (engine, transmission, fuel & emissions)
0 — Type
Generic (SAE standard, common to all manufacturers)
1 — Subsystem
Fuel and air metering