my BMW 3 Series F30/F31 (2012-2019) has a check engine light and P0171 code, what’s wrong?

Solution

1. Preparation

• Gather tools and parts before starting the repair.
• Safety warning: Disconnect the battery before working on electrical components.

2. Inspect and Replace Vacuum Hoses

• Sub-steps:
  • Locate the vacuum hoses connected to the intake manifold and other components.
  • Visually inspect for cracks, splits, or loose connections.
  • Replace any damaged hoses with new ones, ensuring they are secured tightly.

3. Clean or Replace MAF Sensor

• Tools Required: MAF cleaner, torx screwdriver
• Sub-steps:
  • Disconnect the electrical connector from the MAF sensor.
  • Remove the MAF sensor from the air intake tube.
  • Clean the sensor with MAF cleaner and allow it to dry completely before reinstalling, or replace it if damaged.

4. Check and Replace Fuel Filter

• Sub-steps:
  • Locate the fuel filter and relieve the fuel pressure.
  • Disconnect the fuel lines from the filter using appropriate tools.
  • Remove the old filter and install a new one, ensuring correct flow direction.
  • Reconnect the fuel lines securely.

5. Test Fuel Pressure

• Tools Required: Fuel pressure gauge
• Sub-steps:
  • Connect the fuel pressure gauge to the fuel rail or Schrader valve.
  • Turn the ignition to the "ON" position without starting the engine and read the fuel pressure.
  • Compare the reading to the manufacturer's specifications; if low, inspect the fuel pump and filter.