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

Solution

1. Preparation

• Gather required tools and parts.
• Disconnect the battery before starting work.
• Raise the vehicle and secure it with jack stands.

2. Inspect and Replace Oxygen Sensors

1. Remove the upstream oxygen sensor:
   • Use an O2 sensor socket to unscrew the sensor from the exhaust manifold.
   • Disconnect the electrical connector.
2. Install the new upstream oxygen sensor:
   • Apply anti-seize compound to the threads.
   • Screw it in by hand, then tighten to 30 Nm (22 lb-ft) with a torque wrench.
   • Reconnect the electrical connector.
3. Repeat for the downstream oxygen sensor.

3. Inspect and Replace Catalytic Converter

1. Remove the catalytic converter:
   • Loosen and remove any bolts securing the catalytic converter using a socket set.
   • Disconnect any exhaust hangers.
   • Carefully remove the catalytic converter from the exhaust system.
2. Install the new catalytic converter:
   • Position the new catalytic converter in place.
   • Reattach all exhaust bolts and tighten to 40 Nm (30 lb-ft).
   • Reconnect any exhaust hangers.

4. Reset the Engine Control Module (ECM)

1. Reconnect the battery.
2. Use the OBD-II scanner to clear the P0420 code and any other stored codes.