my BMW 3 Series E90/E91 (2005-2012) keeps throwing P0171 code, what can I do?

Solution

1. Preparation

• Gather tools and parts required.
• Disconnect the battery before starting repairs for safety.
• Ensure the engine is cool before working on the intake system.

2. Inspect and Repair Vacuum Leaks

• Tools Required: Vacuum gauge, socket set.
• Sub-steps:
  1. Visually inspect all vacuum hoses connected to the intake manifold for cracks or disconnections.
  2. Use a vacuum gauge to check for leaks by connecting it to a vacuum source.
  3. Replace any damaged hoses or gaskets found during inspection.

3. Clean or Replace MAF Sensor

• Tools Required: MAF sensor cleaner, screwdrivers.
• Sub-steps:
  1. Remove the MAF sensor from the air intake duct.
  2. Spray the sensor with MAF cleaner; do not touch the sensor elements.
  3. Allow it to dry completely before reinstalling.
  4. If cleaning does not resolve the issue, replace the MAF sensor.

4. Test and Replace Fuel Injectors (if necessary)

• Tools Required: Fuel injector cleaning kit, multimeter.
• Sub-steps:
  1. Remove the fuel rail to access the injectors.
  2. Inspect injectors for clogs and perform a resistance test with a multimeter.
  3. Clean injectors using a cleaning kit or replace them if they are faulty.
  4. Reassemble the fuel rail and ensure all connections are tight.

5. Check and Replace ECT Sensor

• Tools Required: Socket set, multimeter.
• Sub-steps:
  1. Locate the ECT sensor (usually near the thermostat housing).
  2. Disconnect the electrical connector and check for continuity with a multimeter.
  3. If the sensor is faulty, replace it with a new one and reconnect.