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

Solution

1. Preparation

• Gather tools and parts required for the repair.
• Disconnect the negative battery terminal to prevent electrical shorts.
• Allow the vehicle to cool before working on the exhaust system.

2. Inspect and Replace Oxygen Sensors

• 2.1. Remove the front (pre-catalytic) oxygen sensor:

  • Use an oxygen sensor socket to loosen and remove the sensor.

• 2.2. Install the new oxygen sensor:

  • Apply anti-seize compound on the threads of the new sensor.
  • Torque to manufacturer specifications (typically around 30 ft-lbs).

• 2.3. Repeat for the rear (post-catalytic) oxygen sensor if necessary:

  • Follow the same steps for removal and installation.

3. Inspect and Replace Catalytic Converter

• 3.1. Remove the exhaust system components:
  • Loosen the bolts connecting the catalytic converter to the exhaust manifold and downstream piping.
  • Remove hangers and brackets as needed.
• 3.2. Remove the old catalytic converter:
  • Carefully take out the catalytic converter from its mounting location.
• 3.3. Install the new catalytic converter:
  • Position the new converter in place, ensuring proper alignment with the exhaust system.
  • Tighten the bolts to the specified torque (typically around 30 ft-lbs).

4. Clear Error Codes and Test

• 4.1. Reconnect the battery:
  • Ensure the negative terminal is securely connected.
• 4.2. Use the OBD-II scanner to clear the P0420 code.
• 4.3. Test drive the vehicle:
  • Monitor the vehicle for any reoccurrence of the check engine light and observe performance.