why does my Volkswagen Golf MK7.5 (2020-Present) have a check engine light with code P0171?

Solution

1. Preparation

• Tools Required: OBD-II scanner, multimeter, vacuum gauge, basic hand tools (sockets, wrenches), torque wrench, fuel pressure gauge.
• Disconnect the negative battery terminal to ensure safety while working on electrical components.

2. Inspect and Repair Vacuum Leaks

• Sub-steps:
  1. Visually inspect all vacuum hoses for cracks or disconnections.
  2. Use a smoke machine or vacuum gauge to identify any leaks in the intake manifold or hoses.
  3. Replace any damaged hoses or gaskets found during the inspection.
  4. Ensure all connections are secure and properly fitted.

3. Clean or Replace the MAF Sensor

• Sub-steps:
  1. Disconnect the MAF sensor connector and remove the sensor from the intake.
  2. Use MAF sensor cleaner to clean the sensor element carefully.
  3. Allow it to dry completely before reinstalling.
  4. If the sensor is damaged or cleaning does not resolve the issue, replace it with a new one.

4. Check Fuel System

• Sub-steps:
  1. Use a fuel pressure gauge to check the fuel pressure at the rail. It should match the specifications in the service manual.
  2. If pressure is low, inspect the fuel pump and filter for blockages or failures.
  3. Replace the fuel filter if it hasn’t been changed according to maintenance schedule.
  4. If the pump is faulty, replace it as necessary.

5. Inspect and Test Oxygen Sensors

• Sub-steps:
  1. Locate the upstream and downstream oxygen sensors.
  2. Use a multimeter to check the voltage output of the upstream oxygen sensor (should fluctuate between 0.1V and 0.9V).
  3. If the sensor is not functioning properly, replace it with a new one.