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

Solution

1. Preparation

• Gather tools and parts needed for repair.
• Disconnect the negative battery terminal to prevent electrical shorts.

Tools Required:

• OBD-II scanner
• Fuel pressure gauge
• Socket set
• Torque wrench
• Multimeter
• Cleaning solvent for MAF sensor

2. Inspect and Repair Air Intake System

• Inspect air filter: Remove the air filter housing and check the air filter for dirt and blockages. Replace if necessary.
• Check intake hoses: Visually inspect hoses for cracks or loose connections. Tighten or replace as needed.
• Inspect throttle body: Remove the throttle body and clean it with an appropriate cleaner, ensuring no dirt obstructs airflow.

3. Test and Clean MAF Sensor

• Remove MAF sensor: Carefully detach the MAF sensor from the air intake tube.
• Clean MAF sensor: Using MAF cleaner, spray the sensor elements gently and allow them to dry completely before reinstalling.

4. Check and Replace Fuel Components

• Test fuel pressure: Connect the fuel pressure gauge to the fuel rail and turn the ignition on (do not start the engine). Compare the reading with manufacturer's specifications.
• Replace fuel filter: If pressure is low, consider replacing the fuel filter.
• Inspect/replace fuel injectors: If they are clogged, clean them or replace them if necessary.

5. Reassemble and Clear Codes

• Reinstall any components removed during the inspection and repair.
• Reconnect the negative battery terminal.
• Use the OBD-II scanner to clear the P0171 code from the ECM.