P0171: Système trop pauvre (Ligne 1)
Système trop pauvre (Ligne 1) : ECM has added more than +20% to +25% combined Short-Term and Long-Term Fuel Trim on Bank 1 to maintain stoichiometric λ = 1.0.
| Trouble Code (DTC) | P0171 |
|---|---|
| Official SAE Definition | Système trop pauvre (Ligne 1) |
| Vehicle Subsystem | powertrain |
| Driving Severity | MEDIUM |
Observable Symptoms
- Rough idle or hesitation on acceleration
- Elevated Long-Term Fuel Trim (LTFT > +15%)
- Hard cold starts
Most Probable Root Causes
- Unmetered air leak (vacuum hose, intake manifold gasket, PCV valve)
- Dirty or contaminated Mass Air Flow (MAF) hot-wire sensor
- Low fuel rail pressure or restricted fuel filter/injector
Step-by-Step Diagnostic Procedure
- Check STFT and LTFT at idle vs 2,500 RPM (if fuel trim improves at RPM, suspect vacuum leak)
- Perform smoke test on intake tract and PCV hoses
- Clean MAF sensor element with dedicated MAF cleaner and check fuel rail pressure