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

Solution

1. Preparation

• Gather necessary tools and parts.
• Disconnect the negative terminal of the battery to ensure safety.

2. Inspect and Repair Vacuum Leaks

• Tools Required: Vacuum gauge, socket set
• Visually inspect all vacuum lines and intake manifold gaskets for signs of wear or damage.
• Use a vacuum gauge to test for leaks; repair or replace any damaged hoses or gaskets found.

3. Clean or Replace MAF Sensor

• Tools Required: MAF sensor cleaner, screwdriver
• Disconnect the MAF sensor connector.
• Remove the MAF sensor from the intake duct.
• Clean the sensor using MAF cleaner, ensuring not to touch the sensor element.
• If cleaning does not resolve the issue, replace the MAF sensor with a new one.

4. Check Fuel Delivery

• Tools Required: Fuel pressure gauge
• Connect the fuel pressure gauge to the fuel rail.
• Turn the ignition on (do not start the engine) to check the fuel pressure; it should meet manufacturer specifications (typically around 50-60 PSI for BMW).
• If pressure is low, inspect and replace the fuel pump or fuel filter as necessary.

5. Inspect Throttle Body

• Tools Required: Throttle body cleaner, screwdriver
• Remove the throttle body from the intake manifold.
• Clean the throttle body thoroughly using throttle body cleaner to remove any carbon buildup.
• Reinstall the throttle body, ensuring all gaskets are properly seated.

6. Reconnect Battery and Reset Codes

• Reconnect the negative battery cable.
• Use the OBD-II scanner to clear any stored trouble codes.
• Start the engine and allow it to reach operating temperature.