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

Solution

1. Preparation

• Gather necessary tools and parts.
• Disconnect the battery to ensure safety while working on the electrical systems.
• Raise the vehicle securely on jack stands.

2. Inspect and Replace Oxygen Sensors (if faulty)

• Tools Required: O2 sensor socket, ratchet, torque wrench
• Remove the upstream (pre-catalytic) oxygen sensor first:
  1. Locate the sensor on the exhaust manifold.
  2. Disconnect the electrical connector.
  3. Use an O2 sensor socket to unscrew and remove the sensor.
  4. Install the new sensor and torque it to the manufacturer's specification (usually around 30 Nm).
  5. Reconnect the electrical connector.
• Repeat the process for the downstream (post-catalytic) oxygen sensor if it was found faulty.

3. Inspect and Replace Catalytic Converter (if necessary)

• Tools Required: Socket set, torch, exhaust hanger removal tool
• If the catalytic converter is damaged or not functioning:
  1. Disconnect any exhaust piping connected to the catalytic converter.
  2. Use an exhaust hanger removal tool to detach the converter from its hangers.
  3. Remove the catalytic converter from the vehicle.
  4. Install the new catalytic converter in the reverse order of removal, ensuring proper alignment and sealing.
  5. Reconnect all exhaust pipes and ensure there are no leaks.

4. Clear Codes and Test Drive

• Reconnect the battery.
• Use the OBD-II scanner to clear the P0420 code.
• Start the engine and check for any reoccurring codes.
• Test drive the vehicle under varied conditions to ensure the issue has been resolved.