how to fix P0421 code in Volkswagen Golf Eighth Generation (2020-present)

Solution

1. Preparation

• Gather tools and parts required for the repair. Ensure the vehicle is parked on a flat surface.
• Disconnect the battery to prevent any electrical short circuits during the repair process.

Tools Required:

• OBD-II scanner
• Socket set
• Multimeter
• Torque wrench
• Vehicle lift or jack stands

2. Inspect and Replace Oxygen Sensors (if necessary)

1. Locate the upstream and downstream oxygen sensors.
2. Disconnect the electrical connectors from both oxygen sensors.
3. Use the appropriate socket to remove the oxygen sensors from the exhaust manifold and catalytic converter.
4. Inspect the threads and condition of the sensors. Replace them if they appear damaged or corroded.
5. Apply anti-seize compound to the threads of the new sensors and install them, tightening to manufacturer specifications.
6. Reconnect the electrical connectors to both sensors.

3. Inspect and Replace the Catalytic Converter (if necessary)

1. Visually inspect the catalytic converter for signs of physical damage or blockage.
2. If replacement is needed, remove the heat shield (if applicable) using a socket set.
3. Disconnect the exhaust pipes from both sides of the catalytic converter.
4. Remove the old catalytic converter by unbolting it from the exhaust system.
5. Install the new catalytic converter, ensuring all gaskets are in place, and bolt down securely using the torque specifications provided in the service manual.
6. Reattach any heat shields and reconnect the exhaust pipes.

4. Clear Codes and Test

1. Reconnect the battery once all repairs are complete.
2. Use an OBD-II scanner to clear the P0421 code from the ECM.
3. Start the engine and allow it to reach operating temperature.
4. Take the vehicle for a test drive to ensure the check engine light does not reappear and monitor the performance.