how to fix P0171 fuel trim system lean in BMW 5 Series G30/G31 (2017-2024)?

Solution

1. Preparation

• Gather necessary tools and parts.
• Ensure the vehicle is parked on a level surface and the engine is cool.
• Disconnect the battery to prevent electrical shorts.

2. Inspect for Vacuum Leaks

• Tools Required: Vacuum gauge, smoke machine (optional).
• Visually inspect all intake hoses and connections for cracks or loose fittings.
• Use a smoke machine to introduce smoke into the intake system to identify any leaks.
• Seal any identified leaks with appropriate materials (e.g., hose clamps, silicone sealant).

3. Check Fuel Pressure

• Tools Required: Fuel pressure gauge.
• Locate the fuel rail test port and connect the fuel pressure gauge.
• Turn the ignition on without starting the engine and check the fuel pressure; it should match the specifications in the service manual (usually around 50-60 psi).
• If pressure is low, diagnose the fuel pump, filter, and pressure regulator.

4. Test the MAF Sensor

• Tools Required: Multimeter or scan tool.
• Disconnect the MAF sensor connector.
• Check for proper voltage output (refer to service manual for specific values).
• Clean the MAF sensor with MAF cleaner if it is dirty, or replace it if faulty.

5. Inspect and Clean Fuel Injectors

• Tools Required: Injector cleaning kit (if necessary), fuel injector O-rings.
• Remove the fuel injectors from the fuel rail.
• Inspect them for clogs and replace any that are damaged.
• Clean the injectors using an appropriate cleaning solution and reassemble with new O-rings.

6. Replace Faulty Components

• If any components (MAF sensor, fuel injectors, etc.) are found faulty during inspections, replace them as necessary.
• Reconnect all components securely.