how to fix P0420 code in my BMW 3 Series G20/G21 (2019-2024)

Solution

1. Preparation

• Gather all necessary tools and parts.
• Disconnect the negative battery terminal to ensure safety.
• Raise the vehicle using a jack and secure it with jack stands.

2. Inspect and Replace Oxygen Sensors

• Remove the upstream (pre-catalytic) oxygen sensor:
  • Use an oxygen sensor socket to carefully unscrew the sensor.
  • Disconnect the electrical connector.
• Install the new upstream oxygen sensor:
  • Apply anti-seize compound to the threads of the new sensor.
  • Torque to manufacturer specifications (usually around 30 lb-ft).
  • Reconnect the electrical connector.

3. Inspect and Replace Catalytic Converter

• Remove the exhaust pipe:
  • Unbolt the exhaust flange and remove any hangers securing the pipe.
  • Carefully detach the exhaust pipe from the catalytic converter.
• Install the new catalytic converter:
  • Position the new catalytic converter in place.
  • Torque bolts to manufacturer specifications, typically around 30 lb-ft.
  • Reattach the exhaust pipe and any hangers.

4. Clear Codes and Test

• Reconnect the negative battery terminal.
• Use the OBD-II scanner to clear any stored codes.
• Start the engine and let it run for a few minutes to ensure everything is functioning properly.