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

Solution

1. Preparation

• Tools Required: OBD-II scanner, fuel pressure gauge, socket set, torque wrench, MAF cleaner, vacuum gauge
• Disconnect the negative battery terminal.
• Allow the engine to cool if it has been running.

2. Inspect and Repair Vacuum Leaks

• Sub-steps:
  • Visually inspect all vacuum hoses for cracks or disconnections.
  • Use a vacuum gauge to test for leaks; a reading outside the normal range indicates a leak.
  • Replace any damaged hoses or gaskets as necessary.

3. Check and Clean MAF Sensor

• Sub-steps:
  • Locate the MAF sensor in the air intake duct.
  • Disconnect the electrical connector and remove the sensor using the appropriate socket.
  • Clean the MAF sensor using MAF cleaner; do not touch the sensor element.
  • Reinstall the sensor and reconnect the electrical connector.

4. Fuel System Inspection

• Sub-steps:
  • Connect the fuel pressure gauge to the fuel rail service port.
  • Start the engine and observe the fuel pressure; it should be within the manufacturer’s specifications.
  • If low, check the fuel pump, fuel filter, and fuel lines for clogs or damage. Replace as needed.

5. Inspect Throttle Body

• Sub-steps:
  • Remove the air intake duct to access the throttle body.
  • Inspect for carbon buildup and clean the throttle body using throttle body cleaner.
  • Reinstall the air intake duct securely.

6. Reassemble and Reset Codes

• Reconnect the negative battery terminal.
• Use the OBD-II scanner to clear the P0171 code.
• Start the engine and let it idle for a few minutes.