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

Solution

1. Preparation

• Gather tools and parts.
• Ensure the vehicle is parked on a level surface with the parking brake engaged.
• Disconnect the battery to prevent electrical shorts.

2. Inspect and Replace Oxygen Sensors

1. Locate the upstream and downstream oxygen sensors on the exhaust system.
2. Use an O2 sensor socket to remove the sensors.
   • Tools Required: O2 sensor socket, ratchet, and extensions.
3. Inspect the old sensors for damage or excessive carbon buildup.
4. Install new oxygen sensors, ensuring they are properly tightened to manufacturer specifications (typically 30-40 Nm).
5. Reconnect the battery.

3. Inspect and Replace the Catalytic Converter

1. Remove any heat shields or protective coverings if necessary.
2. Unbolt the catalytic converter from the exhaust system using a socket set.
   • Tools Required: Socket set, breaker bar.
3. Inspect the old catalytic converter for blockages or damage.
4. Install a new catalytic converter, ensuring proper alignment with exhaust flanges and gaskets.
5. Secure the catalytic converter with bolts to the manufacturer's torque specifications (typically around 30-35 Nm).

4. Clear Diagnostic Codes

1. Reconnect the OBD-II scanner to the vehicle.
2. Clear the P0420 code from the vehicle's memory.
3. Perform a test drive to ensure the vehicle is operating normally.