P0171

• Check engine light comes on
• Weak acceleration, poor pulling power
• High fuel consumption
• Rough idle, tendency to stall
• Black smoke from the exhaust (when the mixture is rich)

• Dirty or faulty mass air flow (MAF) or MAP sensor
• Oxygen (lambda) sensor at the end of its life
• Very dirty air filter or a leak in the intake
• Poor contact in sensor connectors, wiring damage

1. Read the P01xx code and any accompanying codes with an OBD-II scanner.
2. Remove and visually check the air filter — replace it if it's very dirty.
3. Remove and clean the MAF sensor (with MAF cleaner spray, without touching it).
4. Watch oxygen sensor signals in live data — look for rich/lean swings.
5. Check the intake for vacuum leaks (propane or spray test).
6. Clean the sensor connectors and check for corrosion and poor contact.

1. Replace the air filter at the scheduled service interval.
2. Clean the MAF sensor with dedicated spray; replace it if faulty.
3. Replace a faulty MAP sensor.
4. Replace the oxygen (lambda) sensor with a genuine-equivalent part (usually lasts 60,000–100,000 km).
5. Find and repair intake leaks (hoses, gaskets, manifold).
6. Clear the code and watch lambda values in live data at idle and while driving.

• Kia: Bank 1 System Too Lean
• Buick: System Lean Bank 1

• P0170Fuel Trim
• P0172System Too Rich
• P0173Fuel Trim
• P0174System Too Lean
• P0175System Too Rich
• P016CClosed Loop Air/Fuel Ratio Control At Limit - System Too Lean

This page is general information; an exact diagnosis needs measurements and a technician’s check.