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

Solution

1. Preparation

• Gather necessary tools and parts.
• Disconnect the battery to ensure safety while working on electrical components.
• Allow the engine to cool down before starting repairs.

2. Inspect Oxygen Sensors

• Remove the upstream and downstream oxygen sensors using an oxygen sensor socket.
• Inspect the sensors for carbon buildup or damage.
• Replace any faulty sensors with new OEM or high-quality aftermarket sensors.

3. Inspect and Repair Exhaust System

• Check the exhaust system for leaks. Use a smoke machine if necessary to detect leaks.
• Repair or replace any damaged sections of the exhaust system, including flanges, gaskets, or pipes.

4. Inspect and Replace Catalytic Converter (if necessary)

• If the catalytic converter is found to be faulty, it must be replaced.
• Remove the catalytic converter by unbolting it from the exhaust system using a socket set.
• Install the new catalytic converter, ensuring that all gaskets and seals are in place.
• Torque the bolts to manufacturer specifications (typically around 25-30 Nm).

5. Reconnect Battery and Clear Codes

• Reconnect the battery.
• Use the OBD-II scanner to clear the P0420 error code from the ECU.