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

Solution

1. Preparation

• Gather necessary tools and parts.
• Park the vehicle on a level surface and engage the parking brake.
• Disconnect the battery to ensure safety while working on electrical components.

2. Inspect and Replace Oxygen Sensors

• Sub-steps:
  1. Locate the upstream (pre-cat) and downstream (post-cat) oxygen sensors.
  2. Unplug the electrical connectors from both oxygen sensors.
  3. Use an O2 sensor socket to remove the old sensors from the exhaust system.
  4. Install the new oxygen sensors, tightening them to the manufacturer's specified torque (generally around 30-40 Nm).
  5. Reconnect the electrical connectors securely.

3. Inspect and Replace Catalytic Converter (if necessary)

• Sub-steps:
  1. Remove the exhaust heat shield to access the catalytic converter.
  2. Unbolt the catalytic converter from the exhaust manifold and the mid-pipe.
  3. Inspect the catalytic converter for any signs of damage or clogging.
  4. If replacement is needed, install the new catalytic converter, ensuring proper alignment with the exhaust system.
  5. Torque the bolts to the manufacturer's specifications.

4. Clear Error Codes

• Sub-steps:
  1. Reconnect the battery.
  2. Use the OBD-II scanner to clear the P0420 error code.
  3. Start the engine and allow it to reach operating temperature.