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

Solution

1. Preparation

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

2. Inspect and Replace Air Intake Components

• Sub-steps:
  1. Remove the air filter cover and inspect the air filter. Replace if dirty or clogged.
  2. Inspect the intake hoses for cracks or leaks; replace any damaged components.
  3. Clean the MAF sensor using MAF cleaner; do not touch the sensor with fingers.

Tools Required:

• Socket set
• Screwdriver set
• MAF sensor cleaner

3. Check and Replace Fuel System Components

• Sub-steps:
  1. Connect a fuel pressure gauge to the fuel rail and turn the ignition to the "ON" position (do not start the engine) to check fuel pressure.
  2. If pressure is below specifications, replace the fuel filter and check the fuel pump operation.
  3. If the fuel lines are damaged, replace them as needed.

Tools Required:

• Fuel pressure gauge
• Fuel line removal tool

4. Repair Vacuum Leaks

• Sub-steps:
  1. Use a smoke machine or apply soapy water to vacuum hoses to identify leaks.
  2. Replace any faulty vacuum hoses or gaskets found during inspection.

Safety Warnings:

• Ensure the engine is off and cool when working on the intake system to avoid burns.

5. Reassemble and Reconnect

• Sub-steps:
  1. Reinstall any components removed during inspection.
  2. Reconnect the negative battery terminal.

Tools Required:

• Socket set
• Torque wrench (for any reattached components)