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

Solution

1. Preparation

• Gather necessary tools and parts.
• Park the vehicle on a level surface and ensure it is in "Park" or "Neutral" with the parking brake engaged.
• Disconnect the negative battery terminal to prevent electrical shorts.

2. Inspect and Replace O2 Sensors

• Tools Required: O2 sensor socket, ratchet, torque wrench
• Remove the upstream O2 sensor by using the O2 sensor socket.
  • Sub-steps:
    • Disconnect the O2 sensor connector.
    • Use the O2 sensor socket to unscrew the sensor from the exhaust manifold.
• Install the new O2 sensor and torque it to manufacturer's specifications (usually around 30 ft-lbs).
• Reconnect the O2 sensor connector.

3. Check and Replace Catalytic Converter (if necessary)

• Tools Required: Socket set, torque wrench, exhaust pipe cutter (if applicable)
• Inspect the catalytic converter for physical damage or clogging.
• If replacement is needed, remove the old catalytic converter:
  • Sub-steps:
    • Disconnect any exhaust hangers holding the catalytic converter.
    • Use the socket set to remove the bolts connecting the converter to the exhaust system.
    • If necessary, cut the exhaust pipe to remove the converter.
• Install the new catalytic converter, ensuring proper alignment.
  • Torque all bolts to the specified value (check manufacturer specifications).
  • Reattach the exhaust hangers.

4. Reconnect Battery and Clear Codes

• Reconnect the negative battery terminal.
• Use the OBD-II scanner to clear the P0421 code from the system.