Powertrain
generic / SAE
P0171
System Too Lean (Bank 1)
Long-term fuel trim on bank 1 is at the upper limit — the ECU is adding more fuel than baseline to maintain stoichiometric mixture but cannot reach target. Indicates unmetered air entering the intake or insufficient fuel delivery.
SystemPowertrain
Typegeneric / SAE
GroupP0
Range / number1 / 71
Possible causes
- Vacuum leak in intake or PCV system high
- MAF sensor contaminated, under-reading high
- Fuel pressure below specification medium
- Fuel injectors partially clogged medium
Symptoms
- Check engine light on
- Rough idle, possible stalling
- Hesitation or hard cold start
- Power loss under load
Inspection / repair
- Difficulty: medium
- DIY: possible
- Estimated cost: 50–600 €
- Estimated time: 0.5–4 h
- Component: intake manifold
- Component: mass air flow sensor
- Component: fuel pump
- Component: fuel pressure regulator
- Component: fuel injector
- Component: pcv valve
- MIL / check engine light
- emissions-relevant
- drive cycle required
Sources
References
sae:J2012