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

Solution

1. Preparation

• Gather tools and parts needed for the repair.
• Disconnect the negative battery terminal to ensure safety.
• Allow the engine to cool before beginning any work.

2. Inspect and Repair Air Intake System

• Tools Required: Socket set, screwdrivers, vacuum gauge
• Sub-steps:
  1. Remove the engine cover (if applicable) by unscrewing any fasteners.
  2. Inspect all air intake hoses for cracks or loose connections. Tighten or replace as necessary.
  3. Check the air filter; replace it if it is dirty or clogged.
  4. Reinstall the engine cover and reconnect the battery.

3. Test and Clean MAF Sensor

• Tools Required: MAF sensor cleaner
• Sub-steps:
  1. Locate the MAF sensor within the air intake duct.
  2. Disconnect the electrical connector and remove the sensor from its housing.
  3. Spray the MAF sensor with the cleaner, allowing it to dry completely.
  4. Reinstall the MAF sensor and reconnect the electrical connector.

4. Check Fuel Pressure and Injectors

• Tools Required: Fuel pressure gauge, injector cleaner
• Sub-steps:
  1. Attach the fuel pressure gauge to the fuel rail and turn the ignition to the ON position (do not start the engine).
  2. Compare the reading with manufacturer specifications; it should typically be within a range specified in the service manual.
  3. If pressure is low, check the fuel pump and filter for issues.
  4. If necessary, use injector cleaner to clean the fuel injectors.