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

Solution

1. Preparation

• Gather all necessary tools and parts.
• Disconnect the battery to ensure safety during the repair.
• Lift the vehicle securely using jack stands if accessing the undercarriage.

2. Inspect and Replace Oxygen Sensors

• Sub-steps:
  1. Locate the upstream (pre-catalytic) and downstream (post-catalytic) oxygen sensors.
  2. Use an O2 sensor wrench to carefully remove the sensors from their respective locations.
  3. Inspect the threads and connectors for damage and replace if necessary.
  4. Install new oxygen sensors (ensure they are compatible with the BMW G30/G31).
  5. Torque the oxygen sensors to the manufacturer's specifications (typically around 30 Nm).

3. Inspect and Replace Catalytic Converter

• Sub-steps:
  1. Remove the exhaust heat shield if applicable.
  2. Disconnect the exhaust pipes from the catalytic converter using a socket set; ensure to keep any gaskets for reuse.
  3. Remove the catalytic converter from its mounting points.
  4. Inspect the mounting surfaces for any debris or damage; clean if necessary.
  5. Install the new catalytic converter (ensure it is the correct part for the G30/G31).
  6. Torque the exhaust connections to the specified values (usually around 25-35 Nm for exhaust flanges).

4. Reassemble and Connect Battery

• Sub-steps:
  1. Reattach the exhaust heat shield if removed.
  2. Reconnect the battery terminals, ensuring a secure fit.
  3. Start the vehicle and allow it to idle, checking for any exhaust leaks or abnormal sounds.