how to fix P0420 code on my BMW 3 Series F30/F31 (2012-2019)?

Solution

1. Preparation

• Gather tools and parts.
• Ensure the vehicle is parked on a level surface with the engine off and cool.
• Disconnect the battery to prevent any electrical issues during repair.

2. Inspect and Replace Oxygen Sensors

• Sub-steps:
  1. Locate the upstream (pre-catalytic) and downstream (post-catalytic) oxygen sensors.
  2. Disconnect the electrical connectors from both sensors.
  3. Use a socket wrench to remove the oxygen sensors from the exhaust system.
  4. Install new oxygen sensors, tightening them to the manufacturer's specified torque (typically around 25 Nm).
  5. Reconnect the electrical connectors.

3. Inspect and Replace the Catalytic Converter

• Sub-steps:
  1. Elevate the vehicle using jack stands for access to the exhaust system.
  2. Remove the bolts securing the catalytic converter to the exhaust manifold and exhaust pipe.
  3. Carefully remove the catalytic converter from the exhaust system.
  4. Install the new catalytic converter, making sure to align it correctly.
  5. Torque the bolts to the manufacturer’s specifications (usually around 30 Nm).

4. Clear Codes and Test Drive

• Sub-steps:
  1. Reconnect the battery.
  2. Use the OBD-II scanner to clear any stored codes.
  3. Start the engine and allow it to reach operating temperature.
  4. Take the vehicle for a test drive to ensure the check engine light does not reappear.