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

Solution

1. Preparation

• Gather all necessary tools and parts.
• Disconnect the battery to prevent electrical issues.
• Raise the vehicle securely on jack stands.

2. Inspect and Replace Oxygen Sensors

• Tools Required: O2 sensor socket, wrench set, torque wrench.
• Remove the pre-catalytic and post-catalytic oxygen sensors using the O2 sensor socket.
• Inspect the sensor connectors for corrosion; clean if necessary.
• Install new oxygen sensors, ensuring they are torqued to the manufacturer’s specifications (usually around 30 Nm).

3. Examine and Replace Catalytic Converter

• Tools Required: Wrench set, cutting tool (if necessary), gasket scraper, torque wrench.
• Disconnect the exhaust pipe from the catalytic converter, using a cutting tool if it is welded.
• Remove the catalytic converter from the vehicle, checking for any signs of damage or clogging.
• Install the new catalytic converter, ensuring all gaskets are replaced and torqued to specifications (usually around 40 Nm).

4. Clear Codes and Test

• Connect the battery and start the vehicle.
• Use the OBD-II scanner to clear the P0420 code.
• Conduct a test drive under various conditions to ensure the code does not reappear.