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

Solution

1. Preparation

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

2. Inspect and Replace Faulty Oxygen Sensors

• Tools Required: O2 sensor socket, wrench, multimeter.
• Using the O2 sensor socket, remove the upstream (pre-catalytic) oxygen sensor.
• Inspect the sensor for any signs of damage or contamination.
• If faulty, replace it with a new OEM oxygen sensor, tightening it to the manufacturer's specifications (typically around 30 Nm).
• Repeat the process for the downstream (post-catalytic) oxygen sensor if it has also shown signs of failure.

3. Inspect and Replace the Catalytic Converter

• Tools Required: Socket set, torque wrench, exhaust hangers tool.
• Remove the exhaust pipes connected to the catalytic converter using a socket set.
• Carefully unbolt the catalytic converter from the exhaust manifold and remove it from the vehicle.
• Inspect the old catalytic converter for signs of blockage, damage, or contamination.
• Install a new catalytic converter, ensuring it is the correct part for the BMW 5 Series (G30/G31) and torque the bolts to specifications (typically 25 Nm).
• Reconnect all exhaust pipes and components securely.

4. Clear Codes and Test Drive

• Reconnect the battery and use the OBD-II scanner to clear the P0420 code and any related codes.
• Start the engine and allow it to reach operating temperature.
• Take the vehicle for a test drive under various conditions to ensure proper operation and monitor for any reoccurrence of the check engine light.