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

Solution

1. Preparation

• Gather tools and parts required for the repair.
• Disconnect the negative battery terminal to ensure safety during repairs.

2. Inspect and Repair Vacuum Leaks

• Tools Required: Socket set, pliers, vacuum gauge.
• Inspect all vacuum hoses connected to the intake manifold for cracks or disconnections.
• Use a vacuum gauge to check for proper readings. If the gauge indicates a leak, replace any damaged hoses or gaskets.
• Reconnect all hoses securely.

3. Clean or Replace the MAF Sensor

• Tools Required: MAF sensor cleaner or isopropyl alcohol, screwdriver.
• Remove the MAF sensor from the intake pipe.
• Spray the MAF sensor with MAF cleaner, ensuring the delicate wires are not touched. Allow it to dry completely.
• Reinstall the MAF sensor and reconnect the electrical connector.

4. Check and Adjust Fuel System

• Tools Required: Fuel pressure gauge.
• Attach the fuel pressure gauge to the fuel rail service port.
• Turn the ignition to the "ON" position without starting the engine and check the pressure. It should match the specifications in the service manual (typically around 50-60 psi).
• If pressure is low, inspect and replace the fuel filter and/or fuel pump if necessary.

5. Inspect Fuel Injectors

• Tools Required: Fuel injector cleaning kit (optional), multimeter.
• Use a multimeter to check the resistance of each injector (should be around 12-16 ohms).
• If any injectors are out of spec, replace them. Consider cleaning them if they are dirty.

6. Exhaust System Inspection

• Tools Required: Visual inspection tools.
• Inspect the exhaust system for leaks, especially before the oxygen sensors. Use a smoke test if necessary to identify leaks.
• Repair any leaks found in the exhaust system.