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

Solution

1. Preparation

• Gather necessary tools and parts.
• Ensure the vehicle is parked on a flat surface and the engine is cool.
• Disconnect the negative battery cable to prevent electrical shock.

2. Inspect and Replace Oxygen Sensors

• Tools Required: O2 sensor socket, ratchet, torque wrench
• Locate the upstream (pre-catalytic) oxygen sensor and the downstream (post-catalytic) oxygen sensor.
• Use the O2 sensor socket to unscrew the upstream sensor; replace it with a new sensor. Torque to manufacturer specifications (usually around 30 Nm).
• Repeat the process for the downstream sensor if testing indicates it is faulty.

3. Inspect and Repair Exhaust Leaks

• Visually inspect the exhaust system from the engine to the tailpipe for any leaks, cracks, or holes.
• If leaks are found, use exhaust sealant or replace the damaged section of the exhaust system as necessary.

4. Replace the Catalytic Converter (if needed)

• Tools Required: Wrench set, torque wrench, exhaust hangers tool
• Remove any components obstructing access to the catalytic converter (heat shields, clamps).
• Unbolt the catalytic converter from the exhaust manifold and the exhaust pipe.
• Install the new catalytic converter, ensuring proper alignment.
• Bolt it securely and torque to manufacturer specifications.

5. Clear Codes and Test Drive

• Reconnect the negative battery cable.
• Use the OBD-II scanner to clear the P0421 code from the engine control module (ECM).
• Test drive the vehicle under various conditions to ensure the issue is resolved and that the check engine light does not reappear.