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

Solution

1. Preparation

• Gather required tools and parts.
• Disconnect the battery to prevent electrical shorts.
• Raise the vehicle securely on jack stands.

2. Inspect and Replace Oxygen Sensors

1. Locate Oxygen Sensors: Identify the upstream (pre-catalytic converter) and downstream (post-catalytic converter) oxygen sensors.
2. Remove Old Sensors: Use an oxygen sensor socket to carefully remove both sensors.
3. Inspect Connectors: Check electrical connectors for corrosion or damage; replace if necessary.
4. Install New Sensors: Apply anti-seize compound to the threads of the new sensors, then install and torque to manufacturer specifications (typically around 30 Nm).
5. Reconnect Electrical Connectors: Ensure all connections are secure.

3. Inspect and Replace Catalytic Converter (if necessary)

1. Remove Exhaust Components: If the catalytic converter needs replacement, disconnect any exhaust pipes or brackets connected to it.
2. Remove Catalytic Converter: Unbolt the catalytic converter from the exhaust system. Use penetrating oil if bolts are rusted.
3. Install New Catalytic Converter: Position the new catalytic converter and secure it with bolts. Torque to manufacturer specifications (typically around 40 Nm).
4. Reassemble Exhaust Components: Reattach any disconnected exhaust components and ensure gaskets are replaced.

4. Clear Fault Codes

• Reconnect the battery and use an OBD-II scanner to clear any fault codes.
• Start the engine and let it idle for a few minutes.