why does my Volkswagen Passat B8 (2015-2022) have a check engine light with code P0171?

Solution

1. Preparation

• Gather necessary tools and parts.
• Ensure the vehicle is parked on a level surface and the engine is cool.
• Disconnect the battery to prevent electrical shorts.

2. Inspect and Repair Vacuum Leaks

• Tools Required: Vacuum gauge, hose clamps, screwdriver.
• Instructions:
  1. Use a vacuum gauge to check for any discrepancies in vacuum readings.
  2. Visually inspect all vacuum lines for cracks or disconnections.
  3. Replace any damaged hoses or reattach loose connections.
  4. Check the intake manifold gasket for leaks and replace if necessary.

3. Clean or Replace MAF Sensor

• Tools Required: MAF sensor cleaner, torque wrench.
• Instructions:
  1. Locate the MAF sensor in the intake duct.
  2. Disconnect the electrical connector and remove the sensor.
  3. Clean the sensor with MAF cleaner (do not touch the sensing element).
  4. Reinstall the sensor and reconnect the electrical connector. If defective, replace the sensor.

4. Inspect Fuel Delivery System

• Tools Required: Fuel pressure gauge, socket set.
• Instructions:
  1. Attach the fuel pressure gauge to the fuel rail.
  2. Start the engine and check the fuel pressure against manufacturer specifications.
  3. If the pressure is low, inspect or replace the fuel pump and fuel filter.
  4. If necessary, test the fuel pressure regulator for functionality.

5. Check Oxygen Sensors

• Tools Required: OBD-II scanner, multimeter.
• Instructions:
  1. Use the OBD-II scanner to monitor live data from the oxygen sensors.
  2. Check the voltage output of the pre-cat sensor; it should fluctuate between 0.1V and 0.9V.
  3. If the readings are stable or outside this range, replace the faulty sensor.