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

Solution

1. Preparation

• Gather all necessary tools and parts.
• Disconnect the negative battery terminal to ensure safety.
• Make sure the engine is cool before starting work.

2. Inspect and Replace MAF Sensor

1. Locate the MAF sensor in the air intake duct.
2. Disconnect the electrical connector from the MAF sensor.
3. Remove the screws or clamps securing the MAF sensor to the intake duct.
4. Inspect the MAF sensor for dirt or damage; clean it with MAF sensor cleaner if dirty or replace it if damaged.
5. Reinstall the MAF sensor and reconnect the electrical connector.

3. Check and Repair Vacuum Leaks

1. With the engine running, use a smoke machine or carburetor cleaner to identify vacuum leaks around hoses and gaskets.
2. Replace any damaged or cracked hoses and gaskets found during inspection.
3. Ensure all connections are tight and secure.

4. Inspect Fuel System

1. Check the fuel pressure using a fuel pressure gauge. Compare the reading to the manufacturer specifications.
2. If the pressure is low, replace the fuel filter and test the fuel pump for proper operation.
3. Inspect the fuel pressure regulator for leaks or malfunction.

5. Reset Engine Control Module (ECM)

1. Reconnect the negative battery terminal after completing repairs.
2. Start the engine and allow it to reach operating temperature.
3. Use an OBD-II scanner to clear the P0171 code from the ECM.