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

Solution

1. Preparation

• Gather necessary tools and parts.
• Disconnect the negative battery terminal to ensure safety.

2. Inspect and Replace Oxygen Sensors (if faulty)

1. Locate the oxygen sensors: Identify the upstream (pre-catalytic converter) and downstream (post-catalytic converter) O2 sensors.
2. Remove the O2 sensors: Use an oxygen sensor socket and ratchet to unscrew the sensors.
3. Install new sensors: Apply anti-seize compound on the threads of the new sensors and install them by hand.
4. Torque specifications: Tighten to the manufacturer's recommended torque (typically around 30 Nm or 22 lb-ft).

3. Inspect and Replace Catalytic Converter (if necessary)

1. Remove the exhaust: Loosen and remove the bolts securing the exhaust system to access the catalytic converter.
2. Disconnect the catalytic converter: Unbolt it from the exhaust manifold and the mid-pipe.
3. Install new catalytic converter: Position the new converter and secure it with bolts, ensuring proper alignment.
4. Torque specifications: Tighten bolts to manufacturer's specifications (consult service manual for exact values).

4. Clear Error Codes

1. Reconnect the battery: Reconnect the negative terminal.
2. Use OBD-II scanner: Clear the P0420 code from the vehicle's computer system.

5. Final Inspection

1. Check for leaks: Start the engine and inspect exhaust joints for leaks.
2. Test drive: Drive the vehicle under various conditions to ensure the check engine light does not reappear.