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

Solution

1. Preparation

• Gather necessary tools and parts.
• Disconnect the battery to prevent electrical shorts.
• Allow the engine to cool before beginning work on the exhaust system.

2. Inspect and Replace Oxygen Sensors

• Tools Required: O2 sensor socket, torque wrench.
• Remove the upstream and downstream oxygen sensors using the O2 sensor socket.
• Inspect the connectors for corrosion or damage; clean or replace as necessary.
• Install new oxygen sensors and torque them to the manufacturer's specifications (typically around 30 Nm).

3. Inspect the Catalytic Converter

• Tools Required: Jack and jack stands, exhaust pipe cutter or saw (if replacement is necessary).
• Raise the vehicle and secure it on jack stands.
• Visually inspect the catalytic converter for any signs of damage, such as dents or excessive heat discoloration.
• If replacement is necessary, cut the exhaust pipes using the exhaust pipe cutter or saw and remove the old catalytic converter.
• Install the new catalytic converter, ensuring proper sealing and alignment, then secure the exhaust pipes.

4. Clear Codes and Test Drive

• Reconnect the battery and use the OBD-II scanner to clear the P0420 code.
• Conduct a test drive to allow the vehicle to reach operating temperature and monitor for any reoccurring codes.