how to fix P0420 code in BMW 5 Series G30/G31 (2017-2024)

Solution

1. Preparation

• Gather all necessary tools and parts.
• Disconnect the negative battery terminal to prevent electrical shorts.

2. Inspect and Replace Oxygen Sensors (if faulty)

1. Locate the upstream (pre-catalytic) and downstream (post-catalytic) oxygen sensors.
2. Use a socket wrench to remove the faulty oxygen sensor(s).
   • Tools Required: Oxygen sensor socket, ratchet, and extensions.
3. Install the new oxygen sensor(s) by hand to avoid cross-threading and then tighten to the manufacturer's specified torque (typically 30 Nm).
4. Reconnect the electrical connectors.

3. Check and Replace the Catalytic Converter (if necessary)

1. If the catalytic converter shows signs of damage or if the oxygen sensors are functioning properly, proceed to replace the catalytic converter.
2. Remove the exhaust pipes connected to the catalytic converter using a socket set.
   • Tools Required: Socket set, torque wrench.
3. Remove any mounting brackets or bolts holding the catalytic converter in place.
4. Install the new catalytic converter, ensuring proper alignment with the exhaust system.
5. Reattach all bolts and connections, tightening them to the manufacturer's specified torque (typically 40-50 Nm).
6. Reconnect any sensors or electrical connectors removed during the installation.

4. Clear Codes and Test

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