why does my Volkswagen Golf MK5 (2004-2008) have a check engine light with code P0171

Solution

1. Preparation

• Gather tools: OBD-II scanner, multimeter, fuel pressure gauge, vacuum gauge, socket set, and screwdrivers.
• Ensure the vehicle is parked on a level surface and the engine is cool.

2. Inspect and Replace Vacuum Lines

• Sub-steps:
  1. Visually inspect all vacuum hoses connected to the intake manifold and other components.
  2. Replace any damaged or cracked hoses with new vacuum lines.
  3. Use hose clamps to secure the new hoses properly.

3. Clean or Replace the MAF Sensor

• Sub-steps:
  1. Disconnect the electrical connector from the MAF sensor.
  2. Remove the MAF sensor from the intake duct (usually held by screws or clamps).
  3. Clean the MAF sensor with MAF cleaner spray; do not touch the sensor elements.
  4. If cleaning does not resolve the issue, replace the MAF sensor with a new one.

4. Check and Adjust Fuel Pressure

• Sub-steps:
  1. Locate the fuel rail and connect the fuel pressure gauge.
  2. Turn the ignition to the "ON" position (do not start) to prime the fuel system and check the pressure.
  3. If pressure is below specifications (typically 50-60 psi), inspect the fuel pump and filter.
  4. Replace the fuel filter if it’s clogged; if the pump is faulty, replace it.

5. Inspect Fuel Injectors

• Sub-steps:
  1. Remove the engine cover if necessary to access the fuel injectors.
  2. Use a fuel injector cleaning kit or replace the injectors if they are found to be faulty.
  3. Ensure proper seating and that the O-rings are intact when reinstalling.