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

Solution

1. Preparation

• Gather necessary tools and parts.
• Disconnect the vehicle battery to ensure safety.
• Allow the engine to cool before starting work.

2. Inspect and Repair Air Intake System

• Sub-steps:
  1. Remove the engine cover and air intake duct.
  2. Inspect the intake manifold and vacuum hoses for cracks or leaks.
  3. Replace any damaged hoses or gaskets as necessary.
• Tools Required: Socket set, screwdrivers.

3. Clean or Replace MAF Sensor

• Sub-steps:
  1. Disconnect the MAF sensor from its electrical connector.
  2. Remove the sensor from the air intake duct.
  3. Clean the MAF sensor with MAF cleaner; do not touch the sensor elements.
  4. If damaged, replace the MAF sensor with a new one.
• Tools Required: Torx screwdriver, MAF cleaner.

4. Test and Repair Fuel System

• Sub-steps:
  1. Connect a fuel pressure gauge to the fuel rail.
  2. Start the engine and monitor fuel pressure; it should meet specifications (typically around 50-60 psi for BMW).
  3. If pressure is low, check the fuel pump and replace it if necessary.
  4. Inspect the fuel filter and replace if clogged.
• Tools Required: Fuel pressure gauge, socket set.

5. Inspect and Clean Fuel Injectors

• Sub-steps:
  1. Remove the fuel rail to access the injectors.
  2. Inspect the fuel injectors for clogs or damage.
  3. Clean the injectors using an ultrasonic cleaner or replace them if defective.
• Tools Required: Fuel rail removal tool, ultrasonic cleaner (if cleaning).