how to fix the P0171 lean code in my BMW 3 Series E90/E91

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 and Repair Air Intake System

• Sub-steps:
  • Remove the engine cover and air intake duct.
  • Visually inspect for cracks or loose fittings in the intake hoses and manifold.
  • Replace any damaged hoses or seals.
• Tools Required: Socket set, screwdriver set.

3. Clean or Replace MAF Sensor

• Sub-steps:
  • Disconnect the MAF sensor electrical connector.
  • Remove the MAF sensor from the intake system.
  • Clean the sensor using MAF cleaner spray, or replace it if damaged.
• Tools Required: Torx screwdriver, MAF cleaner spray.

4. Check and Adjust Fuel Pressure

• Sub-steps:
  • Locate the fuel rail and connect a fuel pressure gauge.
  • Turn the ignition to the "on" position (do not start) to check pressure readings.
  • If pressure is below specifications, inspect the fuel pump and filter for issues.
• Tools Required: Fuel pressure gauge, socket set.

5. Inspect Fuel Injectors

• Sub-steps:
  • Remove the fuel rail from the engine.
  • Check the injectors for clogs or leaks; clean or replace them as necessary.
• Tools Required: Socket set, injector cleaning kit.

6. Reassemble and Reconnect Battery

• Sub-steps:
  • Reinstall all components in reverse order of removal.
  • Reconnect the battery terminals.
• Tools Required: Socket set.