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

Solution

1. Preparation

• Gather tools and parts required.
• Disconnect the negative battery terminal to prevent electrical short circuits.

2. Inspect and Replace Oxygen Sensors

• Tools Required: O2 sensor socket, wrench, multimeter.

• Remove the pre-catalytic oxygen sensor:

  • Locate the sensor upstream of the catalytic converter.
  • Use the O2 sensor socket to unscrew and remove the sensor.

• Install the new oxygen sensor:

  • Apply anti-seize compound to the threads of the new sensor.
  • Screw it into the exhaust pipe and tighten to manufacturer specifications (usually around 30-35 Nm).

• Repeat the process for the post-catalytic oxygen sensor if needed.

3. Inspect and Replace Catalytic Converter (if necessary)

• Tools Required: Socket set, torque wrench.

• Disconnect exhaust pipes:

  • Support the vehicle securely on jack stands.
  • Use a socket set to remove bolts connecting the catalytic converter to the exhaust system.

• Remove the old catalytic converter:

  • Check for any bolts or clamps that may be holding it in place.
  • Carefully detach the catalytic converter.

• Install the new catalytic converter:

  • Position the new converter in place.
  • Reattach all bolts and connections, tightening them to manufacturer specifications (usually around 30-40 Nm).

4. Clear Codes and Test Drive

• Reconnect the negative battery terminal.
• Use the OBD-II scanner to clear the P0420 code.
• Start the engine and allow it to reach operating temperature.
• Perform a test drive to ensure the check engine light does not reappear.