my BMW 3 Series E90/E91 (2005-2012) has a P0171 code, what does it mean?

Solution

1. Preparation

• Gather all required tools and parts.
• Disconnect the negative battery terminal to prevent electrical shorts.
• Allow the engine to cool down before proceeding with repairs.

2. Inspect Air Intake System

• Remove the air intake duct and visually inspect for cracks or loose connections.
• Replace any damaged hoses or components.
• Reinstall the air intake duct securely.

3. Fuel Pressure Check

• Connect the fuel pressure gauge to the fuel rail.
• Turn the ignition to the ON position (without starting the engine) to check the fuel pressure.
• If the pressure is below specification, check the fuel pump and filter for issues.
• Replace the fuel filter if clogged, and if the pump is faulty, replace it.

4. Clean or Replace MAF Sensor

• Disconnect the MAF sensor electrical connector.
• Remove the MAF sensor from the air intake.
• Clean the sensor with MAF sensor cleaner or replace it if damaged.
• Reinstall the sensor and reconnect the electrical connector.

5. Check Fuel Injectors

• Use a multimeter to check the resistance of each injector; refer to manufacturer specifications.
• If any injector is out of range, replace it.
• If they are functioning, ensure there are no leaks and clean the injectors if necessary.

6. Inspect Oxygen Sensors

• Check the wiring and connections to the oxygen sensors for damage.
• Use a scan tool to monitor the oxygen sensor readings; replace any faulty sensors.
• Reconnect all components and the battery terminal.