how to fix P0171 lean code in BMW 3 Series E90/E91 (2005-2012)?

Solution

1. Preparation

• Gather tools and parts needed for the repair.
• Disconnect the battery to ensure safety while working on electrical components.
• Allow the engine to cool down before starting work.

2. Inspect for Vacuum Leaks

• Sub-steps:
  1. Visually inspect all vacuum lines connected to the intake manifold and throttle body.
  2. Use a smoke machine to introduce smoke into the intake system to identify leaks.
  3. Replace any damaged hoses or gaskets found during the inspection.
• Tools Required: Smoke machine, flashlight, basic hand tools.

3. Clean or Replace MAF Sensor

• Sub-steps:
  1. Disconnect the wiring harness from the MAF sensor.
  2. Remove the MAF sensor from the intake duct.
  3. Clean the sensor with MAF cleaner spray. If damaged, replace with a new one.
  4. Reinstall the sensor and reconnect the wiring harness.
• Tools Required: Torx screwdriver, MAF cleaner spray.

4. Check Fuel Pressure

• Sub-steps:
  1. Locate the fuel rail and attach a fuel pressure gauge to the service port.
  2. Turn the ignition to the "ON" position (do not start) to check the pressure reading.
  3. Ensure the pressure meets manufacturer specifications (typically around 50-60 psi).
  4. If the pressure is low, check the fuel pump, filter, and relay for issues.
• Tools Required: Fuel pressure gauge.

5. Inspect 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; ensure they are within specification.
  3. If any injector is faulty, remove and replace it with a new one.
  4. Reinstall all components and connectors securely.
• Tools Required: Multimeter, basic hand tools.