how to fix P0420 code on BMW 3 Series F30/F31 (2012-2019)

Solution

1. Preparation

• Required Tools: OBD-II scanner, multimeter, socket set, torque wrench, safety glasses, jack and jack stands.
• Safety Warning: Disconnect the battery before starting any electrical work. Allow the engine to cool before working on the exhaust system.

2. Inspect and Replace Oxygen Sensors (if faulty)

1. Remove the Negative Battery Terminal: Ensure safety by disconnecting the battery.
2. Locate the Oxygen Sensors: Find the pre-catalytic and post-catalytic oxygen sensors on the exhaust system.
3. Unplug the Sensor Connectors: Carefully unplug the connectors from both sensors.
4. Remove the Sensors: Use an oxygen sensor socket to unscrew and remove the sensors.
5. Install New Sensors: Apply anti-seize compound on the threads of the new sensors, then install them in reverse order.
6. Reconnect the Battery: Reconnect the negative terminal of the battery.

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

1. Raise the Vehicle: Use a jack and jack stands to elevate the vehicle for better access to the exhaust system.
2. Remove Exhaust Brackets and Bolts: Unbolt any supporting brackets and the exhaust flanges connecting the catalytic converter.
3. Remove the Catalytic Converter: Carefully slide the catalytic converter out of the exhaust system.
4. Inspect the New Catalytic Converter: Ensure the new catalytic converter is the correct part for your vehicle.
5. Install the New Catalytic Converter: Position the new catalytic converter in place and secure it with new gaskets and bolts, torquing them to the manufacturer's specifications.
6. Reconnect Any Brackets: Reattach any exhaust brackets removed during installation.

4. Clear Codes and Test Drive

1. Clear the Codes: Use the OBD-II scanner to erase the P0420 code from the system.
2. Test Drive the Vehicle: Take the vehicle for a test drive to monitor for any reoccurrence of the code.