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.
• Lift the vehicle using jack stands for better access to the exhaust system.

2. Inspect and Replace Oxygen Sensors

• Tools Required: O2 sensor socket, ratchet, torque wrench.
• Remove the upstream (pre-catalytic) oxygen sensor by turning it counterclockwise.
  • Warning: Ensure the exhaust system is cool to avoid burns.
• Install the new oxygen sensor and torque it to manufacturer specifications (usually around 30 Nm).
• Repeat the process for the downstream (post-catalytic) oxygen sensor if needed.

3. Check and Replace Catalytic Converter (if faulty)

• Tools Required: Socket set, exhaust clamp tool (if applicable).
• Remove the exhaust pipes connected to the catalytic converter.
• Detach any brackets or hangers securing the catalytic converter.
• Remove the old catalytic converter and install the new one in reverse order.
• Ensure all connections are secure and reattach any clamps or brackets.

4. Clear Error Codes

• Reconnect the vehicle battery.
• Use the OBD-II scanner to clear the P0420 code from the vehicle's memory.