my BMW 3 Series G20/G21 (2019-2024) has a check engine light and the code is P0171, what to check?

Solution

1. Preparation

• Gather necessary tools and parts.
• Disconnect the battery to ensure safety while working on electrical systems.
• Allow the engine to cool down before starting work.

2. Inspect and Repair Vacuum Leaks

• Sub-steps:
  • Visually inspect all vacuum hoses and gaskets for cracks or disconnections.
  • Use a smoke machine or carburetor cleaner to check for leaks; if the engine RPM changes when sprayed, a leak is present.
  • Replace any damaged hoses or gaskets as needed.

3. Clean the Mass Air Flow Sensor

• Sub-steps:
  • Locate the MAF sensor in the air intake duct.
  • Disconnect the electrical connector and remove the sensor using a Torx screwdriver.
  • Spray MAF sensor cleaner on the sensing element and allow it to dry completely before reinstalling.
  • Reconnect the electrical connector and ensure a tight fit.

4. Check Fuel Pressure

• Sub-steps:
  • Locate the fuel pressure test port on the fuel rail.
  • Connect a fuel pressure gauge to the test port.
  • Turn the ignition to the "ON" position (do not start) and check the pressure reading against manufacturer specifications.
  • If the reading is low, check the fuel pump, fuel filter, and fuel lines for issues.

5. Inspect Fuel Injectors

• Sub-steps:
  • Remove the fuel rail to access the injectors.
  • Inspect each injector for blockage or leaks.
  • Clean the injectors using a specialized injector cleaning kit if necessary.
  • Reinstall the injectors and fuel rail, ensuring all connections are secure.