why does my BMW 3 Series G20/G21 (2019-2024) have a check engine light with code P0171?

Solution

1. Preparation

• Gather necessary tools and parts.
• Disconnect the battery to ensure safety while working on the vehicle.
• Allow the engine to cool down before beginning any repairs.

2. Inspect Air Intake System

• Sub-steps:
  1. Visually inspect the air intake hoses and connections for cracks or loose fittings.
  2. Use a smoke machine to detect any vacuum leaks in the intake system.
  3. Tighten any loose clamps and replace any damaged hoses.

3. Check Mass Airflow Sensor (MAF)

• Sub-steps:
  1. Disconnect the electrical connector from the MAF sensor.
  2. Remove the MAF sensor from the air intake duct.
  3. Clean the sensor with MAF cleaner; avoid touching the sensing elements.
  4. Reinstall the MAF sensor and reconnect the electrical connector.

4. Test Fuel Pressure

• Sub-steps:
  1. Attach a fuel pressure gauge to the fuel rail test port.
  2. Start the engine and check the fuel pressure against OEM specifications.
  3. If the pressure is low, inspect the fuel pump and fuel filter for blockages or failures.

5. Examine Fuel Injectors

• Sub-steps:
  1. Remove the fuel rail with injectors attached.
  2. Inspect each injector for clogs or leaks.
  3. Clean the injectors using a professional cleaning kit if necessary, or replace them if they are faulty.