my Volkswagen Golf MK5 (2004-2008) engine light is on with code P0171, what does it mean?

Solution

1. Preparation

• Gather tools: OBD-II scanner, multimeter, socket set, torque wrench, fuel pressure gauge, and cleaning supplies.
• Ensure the vehicle is parked on a flat surface and the engine is cool.

2. Inspect and Repair the Air Intake System

• Sub-steps:
  1. Visually inspect all vacuum lines and hoses connected to the intake manifold for cracks or disconnects.
  2. If any damaged hoses are found, replace them with OEM parts.
  3. Ensure that the air filter is clean; replace if dirty.

3. Clean or Replace the MAF Sensor

• Sub-steps:
  1. Disconnect the negative battery terminal to prevent electrical shorts.
  2. Locate the MAF sensor in the air intake duct.
  3. Remove the MAF sensor using the appropriate socket size.
  4. Clean the sensor with MAF cleaner spray and allow it to dry completely.
  5. Reinstall the MAF sensor and reconnect the electrical connector.

4. Check and Adjust Fuel Pressure

• Sub-steps:
  1. Connect a fuel pressure gauge to the fuel rail.
  2. Turn the ignition to the "ON" position without starting the engine and check the pressure reading.
  3. If the pressure is below specifications (consult service manual for exact specs), replace the fuel filter or fuel pump as necessary.

5. Inspect and Clean Fuel Injectors

• Sub-steps:
  1. Remove the fuel injectors from the fuel rail.
  2. Use a fuel injector cleaning kit to clean each injector.
  3. Reinstall the cleaned or new injectors and ensure they are seated properly.

6. Test Oxygen Sensors

• Sub-steps:
  1. Use a multimeter to test the voltage output of the upstream oxygen sensor (should fluctuate between 0.1 to 0.9 volts).
  2. Replace the sensor if it shows a constant reading or is out of range.