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

Solution

1. Preparation

• Gather necessary tools and parts.
• Ensure the vehicle is on a flat surface and securely lifted with jack stands if needed.
• Disconnect the battery to prevent electrical shorts.

2. Inspect and Replace Oxygen Sensors

• Tools Required: O2 sensor socket, torque wrench, penetrating oil.
• Sub-steps:
  1. Locate the upstream (pre-catalytic) and downstream (post-catalytic) oxygen sensors.
  2. Use penetrating oil on the sensor threads if they are rusted.
  3. Disconnect the electrical connectors from both sensors.
  4. Remove the sensors using the O2 sensor socket.
  5. Install new sensors, tightening them to the manufacturer's torque specification (typically around 30 ft-lbs).
  6. Reconnect the electrical connectors.

3. Inspect and Replace Catalytic Converter (if necessary)

• Tools Required: Socket set, torque wrench, exhaust gasket, penetrating oil.
• Sub-steps:
  1. Inspect the catalytic converter for physical damage or blockage.
  2. If replacing, disconnect the exhaust pipes from the catalytic converter.
  3. Remove the mounting bolts securing the catalytic converter to the exhaust system.
  4. Remove the old catalytic converter and clean the mounting surfaces.
  5. Install the new catalytic converter with a new gasket, and tighten bolts to the specified torque (typically 30-40 ft-lbs).
  6. Reattach the exhaust pipes securely.

4. Clear Codes and Test Drive

• Sub-steps:
  1. Reconnect the battery.
  2. Use the OBD-II scanner to clear the P0421 code.
  3. Test drive the vehicle under various conditions to ensure proper operation.
  4. Re-scan to confirm the absence of the P0421 code.