my BMW 5 Series F10/F11 (2010-2017) has a check engine light and it's P0420 code

Solution

1. Preparation

• Gather necessary tools and parts, and ensure the vehicle is parked on a level surface.
• Disconnect the battery to prevent electrical shorts.

2. Oxygen Sensor Replacement

• Tools Required: O2 sensor socket, ratchet, torque wrench.
• Remove the oxygen sensor located before the catalytic converter (upstream).
  • Sub-steps:
    • Use the O2 sensor socket to carefully unscrew the sensor.
    • Inspect the threads on the sensor and the exhaust for damage.
    • Install the new upstream O2 sensor, tightening it to the manufacturer’s specified torque (typically around 30 Nm).
    • Reconnect the electrical connector.

3. Catalytic Converter Inspection/Replacement

• Tools Required: Socket set, torque wrench, exhaust hanger removal tool.
• Inspect the catalytic converter for clogs or physical damage.
  • If damage is found, proceed to replace the catalytic converter.
  • Sub-steps:
    • Unbolt the catalytic converter from the exhaust system using the socket set.
    • Remove any exhaust hangers with the exhaust hanger removal tool.
    • Install the new catalytic converter, ensuring proper alignment.
    • Torque all bolts to the manufacturer's specifications (usually around 40 Nm).
    • Reconnect any exhaust hangers and ensure everything is secure.

4. Clear Codes and Test

• Reconnect the battery and use the OBD-II scanner to clear the check engine codes.
• Start the vehicle and allow it to reach operating temperature.