2009 Mitsubishi P0171: What It Means & Is It Safe to Drive?
P0171 on the 2009 Mitsubishi: System Too Lean (Bank 1). Here's what it means, what usually causes it, what repairs typically cost, and whether it's safe to keep driving.
What this code means
The engine is getting too much air relative to fuel. The O2 sensor sees excess oxygen in the exhaust and the PCM is adding more fuel than normal to compensate.
Common causes on the 2009 Mitsubishi
- Dirty or faulty mass airflow (MAF) sensor
- Vacuum leaks (PCV hose, intake gasket, brake booster)
- Weak fuel pump or clogged fuel filter
- Leaking or stuck open fuel injectors (less common)
Symptoms
- Check Engine Light
- Rough idle, hesitation, lack of power
- Possible spark knock under load
- Poor fuel economy
Typical fixes
- Clean or replace MAF sensor
- Locate and seal vacuum leaks
- Replace fuel filter / test fuel pressure
- Smoke test intake system
Repair cost range
For a 2009 Mitsubishi, repairs for P0171 typically fall between $50 and $500, depending on the root cause and labor rates in your area.
Known issues on Mitsubishi
Mitsubishi P0171 on 2.4L 4B12 MIVEC (Outlander, Eclipse Cross) most often traces to MAF sensor contamination—Mitsubishi MAF sensors are sensitive to debris and oil. On Eclipse GT 3.8L 6G75 V6, the intake air temperature sensor alongside the MAF can give incorrect readings and set P0171. On Lancer Evo IX 4G63 turbocharged, a leaking recirculation valve (BOV or BPV) on the charge pipe causes temporary lean conditions under throttle lift; test the recirc valve before chasing lean codes on track-use vehicles.
Most commonly affected models