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

Solution

1. Preparation

• Gather tools and parts required for the repair.
• Disconnect the negative battery terminal to prevent electrical shorts.
• Allow the engine to cool before working on components.

2. Inspect and Repair Vacuum Leaks

• Sub-steps:
  1. Visually inspect all vacuum lines and the intake manifold for cracks or disconnections.
  2. Use a smoke machine or carburetor cleaner to locate leaks.
  3. Replace any damaged hoses or gaskets.

3. Clean or Replace MAF Sensor

• Sub-steps:
  1. Disconnect the MAF sensor electrical connector.
  2. Remove the MAF sensor from the air intake duct.
  3. Clean the sensor using MAF cleaner (do not touch the sensor element).
  4. If cleaning does not resolve the issue, replace the MAF sensor with a new one.
  5. Reinstall the MAF sensor and reconnect the electrical connector.

4. Check Fuel Pressure

• Sub-steps:
  1. Locate the fuel pressure test port on the fuel rail.
  2. Attach a fuel pressure gauge to the test port.
  3. Turn the ignition to the "ON" position (do not start the engine) and read the fuel pressure.
  4. Compare the reading to the manufacturer's specifications (usually around 50-60 psi).
  5. If the pressure is low, inspect the fuel pump and fuel filter for issues.

5. Inspect Fuel Injectors

• Sub-steps:
  1. Remove the fuel rail to access the injectors.
  2. Check for signs of leaks or blockage in the injectors.
  3. Clean the injectors with a specialized cleaner or consider replacing them if faulty.
  4. Reinstall the fuel rail and ensure all connections are secure.

6. Verify Oxygen Sensor Functionality

• Sub-steps:
  1. Use a multimeter to test the voltage signal of the upstream oxygen sensor.
  2. Ensure it fluctuates between 0.1V and 0.9V with engine running.
  3. If the sensor is not functioning correctly, replace it with a new one.
  4. Reconnect any electrical connectors and clear the error codes.