what does it mean if my BMW 3 Series E90/E91 (2005-2012) has a check engine light and P0171 code

Solution

1. Preparation

• Gather necessary tools and parts.
• Disconnect the battery to prevent any electrical issues.
• Ensure the vehicle is on a level surface and secure it with jack stands if necessary.

2. Inspect and Replace Vacuum Hoses

• Sub-steps:
  • Visually inspect all vacuum lines connected to the intake manifold.
  • Replace any damaged or cracked hoses with OEM parts.
• Tools Required: Pliers, hose cutter.

3. Clean or Replace the MAF Sensor

• Sub-steps:
  • Disconnect the MAF sensor connector.
  • Remove the MAF sensor from the air intake duct.
  • Clean the sensor with MAF cleaner (do not use other cleaners).
  • If damage is observed, replace the MAF sensor with a new one.
• Tools Required: Torx screwdriver, MAF cleaner.

4. Inspect and Replace Fuel Filter (if needed)

• Sub-steps:
  • Locate the fuel filter under the vehicle.
  • Relieve fuel system pressure by removing the fuel pump fuse and starting the engine until it stalls.
  • Disconnect the fuel lines from the filter.
  • Replace the old filter with a new one, ensuring correct orientation.
• Tools Required: Wrenches, fuel line disconnect tool.

5. Check Fuel Injectors

• Sub-steps:
  • Remove the engine cover to access fuel injectors.
  • Inspect electrical connectors and wiring for damage.
  • Perform a resistance test using a multimeter to confirm injector function.
  • Replace any faulty injectors with OEM replacements.
• Tools Required: Multimeter, socket set.

6. Inspect Intake Manifold Gasket

• Sub-steps:
  • Remove the intake manifold if necessary to access the gasket.
  • Inspect the gasket for cracks or wear.
  • Replace with a new gasket and reassemble the manifold.
• Tools Required: Torque wrench, gasket scraper.