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

Solution

1. Preparation

• Gather tools and parts required for the repair.
• Disconnect the negative battery terminal to prevent electrical issues.
• Tools Required: OBD-II scanner, multimeter, socket set, jack and jack stands, torque wrench.

2. Inspect and Replace Oxygen Sensors

• Remove the pre-catalytic oxygen sensor using a socket wrench.
• Inspect the sensor for contamination or damage. If faulty, replace it with a new OEM sensor.
• Repeat the process for the post-catalytic oxygen sensor.
• Torque the new sensors to the manufacturer's specifications (typically around 30 Nm).

3. Check or Replace Catalytic Converter

• If the oxygen sensors are functioning correctly and the code persists, inspect the catalytic converter for blockage or damage.
• If a blockage is found, remove the catalytic converter from the exhaust system.
• Replace it with a new OEM catalytic converter following the manufacturer’s specifications.
• Ensure all gaskets and bolts are replaced and torqued to the specified values.

4. Reassemble and Reconnect

• Reinstall any components removed during the inspection.
• Reconnect the negative battery terminal.
• Clear the P0420 code using the OBD-II scanner.