how to fix P0421 code in Volkswagen Golf MK7.5 (2020-Present)

Solution

1. Preparation

• Gather necessary tools and parts.
• Disconnect the negative battery terminal to prevent electrical shorts.
• Allow the vehicle to cool down completely before working on the exhaust system.

2. Inspect and Replace Oxygen Sensors

• Tools Required: O2 sensor socket, torque wrench.
• Disconnect the electrical connectors from the upstream and downstream oxygen sensors.
• Using the O2 sensor socket, remove the old sensors from the exhaust manifold and catalytic converter.
• Install the new sensors, ensuring they are properly torqued to the manufacturer specifications (typically around 30 Nm).
• Reconnect electrical connectors securely.

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

• Tools Required: Socket set, exhaust hanger removal tool, torque wrench.
• Remove any heat shields or components obstructing access to the catalytic converter.
• Unscrew the bolts securing the catalytic converter to the exhaust system using the socket set.
• Carefully remove the catalytic converter, ensuring not to damage any surrounding components.
• Install the new catalytic converter, aligning it with the exhaust system, and torque the bolts to the manufacturer specifications (typically around 25 Nm).
• Reattach any heat shields and components removed earlier.

4. Final Checks

• Reinstall any parts removed during the process.
• Reconnect the negative battery terminal.
• Start the vehicle and allow it to reach operating temperature.