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

Solution

1. Preparation

• Gather all necessary tools and parts.
• Ensure the vehicle is on a level surface and the engine is cool.
• Disconnect the battery to prevent any electrical shorts.

2. Inspect and Replace Oxygen Sensors

1. Remove the downstream oxygen sensor:
   • Use an oxygen sensor socket.
   • Disconnect the electrical connector.
2. Inspect the sensor for signs of wear or damage.
3. If faulty, replace it with a new sensor.
4. Reconnect the electrical connector and install the sensor.

3. Inspect and Replace Catalytic Converter

1. Check for exhaust leaks before the catalytic converter.
2. If the catalytic converter is damaged:
   • Remove the exhaust pipes connected to the catalytic converter using a socket set.
   • Unbolt the catalytic converter from the exhaust manifold.
3. Install the new catalytic converter:
   • Position it in place and secure it with the bolts to the exhaust manifold.
   • Reconnect the exhaust pipes and ensure all connections are tight.

4. Clear the Codes

1. Reconnect the battery.
2. Use the OBD-II scanner to clear the P0420 code from the ECU.
3. Start the engine and let it warm up to operating temperature.