how do I fix the P0171 code on my BMW 3 Series G20/G21 (2019-2024)

Solution

1. Preparation

• Gather tools and parts necessary for repairs.
• Disconnect the negative battery terminal.

Tools Required:

• OBD-II scanner
• Vacuum gauge
• Fuel pressure gauge
• Torque wrench
• Socket set
• MAF sensor cleaner

2. Inspect for Vacuum Leaks

• Visually inspect all vacuum lines and intake gaskets for signs of wear or damage.
• Use a smoke machine or spray a light mist of water around suspected areas while the engine is running to identify leaks.

3. Check Fuel Pressure

• Connect the fuel pressure gauge to the fuel rail.
• Turn the ignition to the "ON" position (do not start) and check the fuel pressure.
• Compare the reading to the manufacturer's specifications (typically around 50-60 psi).
• If pressure is low, inspect the fuel pump and filter for issues.

4. Clean or Replace MAF Sensor

• Locate the MAF sensor in the intake duct.
• Disconnect the electrical connector and remove the sensor using a socket set.
• Clean the MAF sensor with MAF sensor cleaner. Allow it to dry completely before reinstalling.
• If cleaning does not resolve the issue, replace the MAF sensor.

5. Inspect Oxygen Sensors

• Locate the pre-cat and post-cat oxygen sensors.
• Check wiring for frays or disconnections. Use a multimeter to verify sensor operation.
• Replace any faulty sensors.

6. Reassemble and Test

• Reconnect all components, ensuring all connections are tight.
• Reconnect the negative battery terminal.
• Start the engine and allow it to reach operating temperature.