how to fix P0171 lean code in 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.

2. Inspect and Repair Vacuum Leaks

• Sub-steps:
  1. Visually inspect all vacuum hoses connected to the intake manifold for cracks or disconnections.
  2. Use a smoke machine or carb cleaner to identify any leaks by applying it around suspected areas while the engine is running.
  3. Replace any damaged hoses or gaskets found during inspection.

3. Clean or Replace MAF Sensor

• Sub-steps:
  1. Locate the MAF sensor in the air intake duct.
  2. Disconnect the electrical connector and remove the sensor from the duct.
  3. Clean the MAF sensor using MAF cleaner spray, avoiding contact with the sensing elements.
  4. If cleaning does not resolve the issue, replace the MAF sensor with a new one.

4. Check and Replace Fuel Filter (if applicable)

• Sub-steps:
  1. Locate and access the fuel filter, usually found along the fuel line.
  2. Relieve fuel pressure by disconnecting the fuel pump fuse and starting the engine until it stalls.
  3. Disconnect the fuel lines and remove the old fuel filter.
  4. Install the new fuel filter, ensuring proper orientation, and reconnect the fuel lines.

5. Inspect and Test Fuel Injectors

• Sub-steps:
  1. Remove the engine cover to access the fuel injectors.
  2. Use a multimeter to check the resistance of each injector; refer to specifications for proper values.
  3. If any injectors are faulty, replace them with new ones.

6. Reconnect Battery and Clear Codes

• Sub-steps:
  1. Reconnect the negative battery terminal.
  2. Use an OBD-II scanner to clear the P0171 code from the system.
  3. Perform a test drive to ensure the issue is resolved.