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

Solution

1. Preparation

• Gather tools: OBD-II scanner, multimeter, infrared thermometer, socket set, jack and jack stands.
• Disconnect the negative battery terminal to prevent electrical shorts.

2. Inspect and Replace Oxygen Sensors (if necessary)

1. Locate the upstream (pre-catalytic) and downstream (post-catalytic) oxygen sensors.
2. Use a socket wrench to remove the oxygen sensors from the exhaust system.
3. Inspect the sensors for damage or contamination.
4. If faulty, install new oxygen sensors:
   • Apply anti-seize compound to the threads of the new sensors.
   • Torque to manufacturer's specifications (usually around 30 lb-ft).
5. Reconnect the electrical connectors.

3. Inspect and Replace Catalytic Converter (if necessary)

1. Disconnect the exhaust system from the catalytic converter by removing the clamps or bolts.
2. Use a socket set to unbolt the catalytic converter from the exhaust manifold and the exhaust pipe.
3. Inspect the old catalytic converter for any signs of internal damage or clogging.
4. Install the new catalytic converter:
   • Align it and secure it to the exhaust manifold and pipe.
   • Torque the bolts to the specified values (often around 30-40 lb-ft).
5. Reconnect the exhaust system and ensure all clamps are tight.

4. Reset the Engine Control Module (ECM)

1. Reconnect the negative battery terminal.
2. Use an OBD-II scanner to clear the P0420 code from the ECM.
3. Start the engine and let it idle for a few minutes.