BMW 5 Series F10/F11 (2010-2017) engine light on with P0420 code, how to fix?

Solution

1. Preparation

• Gather necessary tools and replacement parts.
• Ensure the vehicle is parked on a level surface and the engine is cool.
• Disconnect the battery to prevent electrical shorts.

2. Inspect and Replace Oxygen Sensors

1. Locate the upstream and downstream oxygen sensors on the exhaust system.
2. Using a socket wrench, carefully remove the oxygen sensors.
3. Inspect the threads for damage; replace if necessary.
4. Install new oxygen sensors, tightening them to the manufacturer's specified torque (typically 30 Nm).
5. Reconnect the battery.

3. Replace Catalytic Converter (if necessary)

1. If the catalytic converter is found to be defective, raise the vehicle securely on jack stands.
2. Remove the bolts securing the catalytic converter to the exhaust manifold and the rear exhaust pipe using a socket set.
3. Carefully detach the old catalytic converter and inspect the exhaust gaskets.
4. Install the new catalytic converter, ensuring proper alignment with the exhaust system.
5. Replace gaskets if damaged and secure with bolts, tightening to the manufacturer's specified torque.

4. Reset the Engine Control Unit (ECU)

1. Use an OBD-II scanner to clear the fault codes from the ECU.
2. Start the engine and allow it to idle for a few minutes to ensure the system is operating correctly.