how to fix P0171 lean code on BMW 3 Series G20/G21 (2019-2024)

Solution

1. Preparation

• Gather tools and parts required.
• Ensure the vehicle is parked on a flat surface and the engine is cool.

2. Inspect and Replace Vacuum Hoses

• Sub-steps:
  • Visually inspect all vacuum hoses for cracks or disconnections.
  • Use a smoke machine or soapy water to detect leaks if necessary.
  • Replace any damaged hoses with OEM parts.

3. Clean or Replace MAF Sensor

• Tools Required: MAF cleaner, screwdriver
• Sub-steps:
  • Disconnect the electrical connector from the MAF sensor.
  • Remove the sensor from the air intake duct.
  • Clean the sensor using MAF cleaner and allow it to dry; if damaged, replace with a new sensor.
  • Reinstall the MAF sensor and reconnect the electrical connector.

4. Check and Replace Fuel Filter

• Tools Required: Fuel line disconnect tool, wrench set, catch pan
• Sub-steps:
  • Relieve fuel system pressure by removing the fuel pump fuse and starting the engine until it stalls.
  • Locate the fuel filter and disconnect the fuel lines using the fuel line disconnect tool.
  • Remove the filter and install a new one, ensuring proper orientation.
  • Reconnect the fuel lines and reinstall the fuel pump fuse.

5. Test Fuel Pressure

• Tools Required: Fuel pressure gauge
• Sub-steps:
  • Connect the fuel pressure gauge to the fuel rail service port.
  • Turn the ignition key to the "ON" position (do not start) to check the pressure reading.
  • Compare the reading with the manufacturer specifications; replace the fuel pump if pressure is low.

6. Inspect PCV System

• Sub-steps:
  • Locate the PCV valve and inspect it for blockages or malfunctions.
  • Replace the PCV valve if necessary.