my BMW 3 Series E90/E91 (2005-2012) has P0171 code what does this mean

Solution

1. Preparation

• Gather tools and parts needed for the repair.
• Disconnect the battery to ensure safety while working on the vehicle.
• Allow the engine to cool before beginning work.

2. Inspect and Repair Air Intake System

• Sub-steps:
  1. Visually inspect all vacuum lines and hoses for cracks or disconnections.
  2. Replace any damaged hoses or connections.
  3. Clean the MAF sensor using a specialized MAF cleaner, ensuring not to touch the sensing elements.

Tools Required:

• Screwdrivers
• Pliers
• MAF cleaner

3. Fuel Pressure Check

• Sub-steps:
  1. Connect the fuel pressure gauge to the fuel rail test port.
  2. Turn the ignition to the "ON" position (do not start) and check the pressure reading.
  3. If pressure is below specifications, consider replacing the fuel pump or fuel filter.

Tools Required:

• Fuel pressure gauge

4. Oxygen Sensor Testing

• Sub-steps:
  1. Disconnect the electrical connector from the upstream oxygen sensor.
  2. Use a multimeter to test the voltage output while the engine is running; voltage should fluctuate between 0.1 to 0.9 volts.
  3. If the readings are out of range, replace the oxygen sensor.

Tools Required:

• Multimeter