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

Solution

1. Preparation

• Gather tools and parts needed for the repair.
• Disconnect the negative battery terminal to ensure safety.

2. Inspect and Repair Air Intake System

• Sub-steps:
  • Remove the engine cover to access the air intake system.
  • Inspect the intake hoses and connections for cracks or loose fittings.
  • Replace any damaged components with OEM parts.
• Tools Required: Socket set, pliers

3. Clean or Replace MAF Sensor

• Sub-steps:
  • Locate the MAF sensor within the intake duct.
  • Disconnect the electrical connector and remove the sensor from the duct.
  • Clean the MAF sensor with MAF cleaner spray. If damaged, replace it.
  • Reinstall the sensor and ensure the connections are secure.
• Tools Required: Screwdriver, MAF cleaner
• Safety Warnings: Avoid touching the sensor elements.

4. Test and Replace Fuel Pump (if necessary)

• Sub-steps:
  • Connect a fuel pressure gauge to the fuel rail test port.
  • Turn the ignition to the "On" position (do not start) and check pressure readings against manufacturer specifications.
  • If pressure is low, access the fuel pump by removing the rear seat or accessing the fuel tank.
  • Replace the fuel pump if it is not functioning properly.
• Tools Required: Fuel pressure gauge, socket set
• Safety Warnings: Relieve fuel pressure before disconnecting lines.

5. Inspect and Clean Fuel Injectors

• Sub-steps:
  • Remove the fuel rail to access the injectors.
  • Inspect each injector for clogs or signs of leakage.
  • Use fuel injector cleaner or replace injectors if they are faulty.
  • Reinstall the fuel rail and ensure all connections are secure.
• Tools Required: Socket set, fuel injector cleaner
• Safety Warnings: Handle fuel injectors carefully to avoid spills.