how to fix P0421 code on Volkswagen Golf MK7 (2015-2019)?

Solution

1. Preparation

• Gather tools and parts required for repair.
• Disconnect the negative battery cable to ensure safety.
• Allow the engine to cool before starting work.

2. Inspect and Replace Oxygen Sensors

• Tools Required: O2 sensor socket, torque wrench
• Sub-steps:
  1. Locate the upstream and downstream oxygen sensors in the exhaust system.
  2. Disconnect the electrical connectors from each sensor.
  3. Remove the sensors using the O2 sensor socket.
  4. Install new oxygen sensors and torque to manufacturer specifications (typically 30-40 lb-ft).
  5. Reconnect the electrical connectors.

3. Examine and Replace Catalytic Converter (if necessary)

• Tools Required: Socket set, exhaust pipe cutter, gaskets, torque wrench
• Sub-steps:
  1. Inspect the catalytic converter for damage. If damaged, proceed with replacement.
  2. Use the exhaust pipe cutter to remove the old catalytic converter from the exhaust system.
  3. Clean the mounting surfaces to ensure a good seal with the new converter.
  4. Position the new catalytic converter and secure it using new gaskets.
  5. Torque the bolts to manufacturer specifications (usually 30-40 lb-ft).

4. Clear Codes and Test

• Tools Required: OBD-II scanner
• Sub-steps:
  1. Reconnect the negative battery cable.
  2. Use the OBD-II scanner to clear the error codes from the vehicle's computer.
  3. Start the engine and allow it to reach operating temperature.
  4. Check for any reoccurring codes after a test drive.