how to resolve P0171 and P0174 codes on my BMW 3 Series E90/E91 (2005-2012)?

Solution

1. Preparation

• Gather tools and parts required for repair.
• Disconnect the vehicle's battery to ensure safety.
• Allow the engine to cool down before starting work.

2. Inspect and Repair Vacuum Leaks

• Sub-steps:
  1. Visually inspect all vacuum hoses connected to the intake manifold for cracks or disconnections.
  2. Use a smoke machine to detect leaks if necessary.
  3. Replace any damaged hoses or gaskets with OEM parts.

Tools Required:

• Smoke machine (optional)
• Pliers

3. Clean or Replace MAF Sensor

• Sub-steps:
  1. Locate the MAF sensor in the air intake duct.
  2. Disconnect the electrical connector and remove the MAF sensor from the duct.
  3. Clean the MAF sensor with MAF cleaner spray or replace it if necessary.
  4. Reinstall the MAF sensor and reconnect the electrical connector.

Tools Required:

• MAF cleaner spray
• Screwdriver set

4. Check Fuel System

• Sub-steps:
  1. Use a fuel pressure gauge to check the fuel pressure at the fuel rail.
  2. If the pressure is low, inspect the fuel pump and filter for issues.
  3. Replace the fuel filter if it is clogged or replace the fuel pump if it’s not delivering proper pressure.

Tools Required:

• Fuel pressure gauge
• Wrench set

5. Inspect and Test Oxygen Sensors

• Sub-steps:
  1. Locate both upstream and downstream oxygen sensors.
  2. Disconnect the sensors and use a multimeter to check their resistance and functionality.
  3. Replace any faulty oxygen sensors with OEM parts.

Tools Required:

• Multimeter
• Oxygen sensor socket