how to fix P0420 code on my BMW 5 Series G30/G31 (2017-2024)

Solution

1. Preparation

• Gather necessary tools and parts.
• Disconnect the battery before starting work.
• Allow the exhaust system to cool completely before inspection.

2. Inspect and Replace Oxygen Sensors (if faulty)

• Step 1: Locate the upstream and downstream oxygen sensors near the catalytic converter.
• Step 2: Disconnect the electrical connectors from both sensors.
• Step 3: Use an oxygen sensor socket to remove the sensors from the exhaust pipe.
• Step 4: Install new oxygen sensors by screwing them in and tightening to the manufacturer's specified torque (typically around 30 Nm).
• Step 5: Reconnect the electrical connectors ensuring a secure fit.

3. Check and Replace the Catalytic Converter (if necessary)

• Step 1: Inspect the catalytic converter for any physical damage or excessive carbon buildup.
• Step 2: If replacement is needed, disconnect the exhaust pipes by removing any clamps or bolts securing it.
• Step 3: Remove the old catalytic converter from the exhaust system.
• Step 4: Install the new catalytic converter, ensuring proper alignment.
• Step 5: Reattach all exhaust clamps and bolts, tightening them to the manufacturer's specifications.

4. Clear Codes and Test Drive

• Step 1: Reconnect the battery.
• Step 2: Use an OBD-II scanner to clear the P0420 code.
• Step 3: Start the engine and allow it to reach operating temperature.
• Step 4: Take the vehicle for a test drive to ensure the check engine light does not reappear.