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 shorts.
• Allow the exhaust system to cool before working on it.

2. Inspect and Replace Oxygen Sensors

• Tools Required: O2 sensor socket, torque wrench, penetrating oil, multimeter.
• Sub-steps:
  1. Locate the upstream and downstream oxygen sensors on the exhaust manifold and catalytic converter.
  2. Apply penetrating oil to the sensor threads and let it sit for a few minutes.
  3. Use the O2 sensor socket to remove the sensors.
  4. Inspect the sensors for damage or contamination; replace if necessary.
  5. Install the new sensors and torque them to the manufacturer's specifications (usually around 30 Nm).

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

• Tools Required: Wrench set, exhaust pipe cutter, gasket scraper, torque wrench.
• Sub-steps:
  1. Remove the exhaust pipes connected to the catalytic converter using the wrench set.
  2. Inspect the catalytic converter for any signs of physical damage or blockage; replace if necessary.
  3. Remove the old catalytic converter and clean the mounting surfaces using a gasket scraper.
  4. Install the new catalytic converter and reconnect the exhaust pipes, tightening them to the appropriate torque specifications.

4. Final Steps

• Reconnect the negative battery terminal.
• Clear the P0420 code using the OBD-II scanner.