my BMW 3 Series E90/E91 (2005-2012) has a check engine light and P0171 code, what should I do?

Solution

1. Preparation

• Gather necessary tools and parts.
• Disconnect the negative battery terminal to ensure safety.

2. Inspect and Repair Air Intake System

• Check air intake hoses for cracks or damage.
• If any hoses are damaged, replace them with new ones.
• Reconnect any loose connections securely.

3. Clean or Replace MAF Sensor

• Remove the MAF sensor from the air intake duct.
• Use MAF sensor cleaner to clean the sensor, following the manufacturer's instructions.
• If cleaning does not resolve the issue, replace the MAF sensor with a new one.

4. Check Fuel System

• Use a fuel pressure gauge to check the fuel pump pressure against manufacturer specifications.
• If pressure is low, inspect the fuel filter and replace it if clogged.
• If the filter is clear, test the fuel pump for proper operation and replace if necessary.

5. Inspect Vacuum Lines

• Visually inspect all vacuum lines for cracks, damage, or disconnections.
• Replace any damaged vacuum lines.

6. Reconnect Battery

• Reconnect the negative battery terminal once all repairs are completed.