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

Solution

1. Preparation

• Gather necessary tools and parts.
• Disconnect the battery to avoid electrical shorts.

2. Inspect and Repair Vacuum Leaks

• Sub-steps:
  • Visually inspect all vacuum hoses connected to the intake manifold.
  • Use a smoke machine or carb cleaner to identify leaks.
  • Replace any damaged or cracked hoses.
• Tools Required: Smoke machine or carb cleaner, screwdriver set.

3. Clean or Replace MAF Sensor

• Sub-steps:
  • Locate the MAF sensor on the air intake duct.
  • Disconnect the electrical connector and remove the sensor from its housing.
  • Clean the sensor using MAF sensor cleaner. Let it dry completely before reinstalling.
  • If damaged, replace with a new MAF sensor.
• Tools Required: Torx or socket set, MAF sensor cleaner.

4. Check and Clean Throttle Body

• Sub-steps:
  • Remove the air intake duct to access the throttle body.
  • Use throttle body cleaner to remove carbon buildup, applying it to a clean cloth or brush.
  • Open the throttle plate manually to clean inside it thoroughly.
  • Reassemble the intake duct.
• Tools Required: Throttle body cleaner, cleaning cloth, screwdriver set.

5. Fuel Pressure Check

• Sub-steps:
  • Locate the fuel rail and connect the fuel pressure gauge.
  • Turn the ignition to the "on" position (do not start) to check fuel pressure.
  • Compare the reading to manufacturer specifications; if low, check the fuel pump and filter.
• Tools Required: Fuel pressure gauge.