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

Solution

1. Preparation

• Gather all necessary tools and parts.
• Disconnect the negative battery terminal to prevent electrical shorts.
• Allow the engine to cool completely if it has been running.

2. Inspect and Replace Oxygen Sensors

• Tools Required: O2 sensor socket, socket set, torque wrench.

• Remove the upstream (pre-catalytic) oxygen sensor:

  1. Use the O2 sensor socket to unscrew the sensor from the exhaust manifold.
  2. Inspect the connector for corrosion or damage; replace if necessary.

• Remove the downstream (post-catalytic) oxygen sensor:

  1. Use the O2 sensor socket again to unscrew the sensor from the catalytic converter.
  2. Check the wiring and connector; replace if damaged.

• Install the new oxygen sensors:

  1. Apply anti-seize compound on the threads of the new sensors.
  2. Screw them in by hand, then tighten to the manufacturer’s specifications (typically around 30 Nm).

3. Inspect and Replace Catalytic Converter (if necessary)

• Tools Required: Socket set, exhaust pipe cutter, jack stands, safety goggles, gloves.

• Raise the vehicle securely on jack stands.

• Remove the exhaust system components leading to the catalytic converter:

  1. Use the socket set to disconnect bolts and brackets.
  2. Cut the exhaust pipe if needed for easier removal.

• Remove the old catalytic converter:

  1. Take out any supporting hardware and carefully remove the catalytic converter from its position.

• Install the new catalytic converter:

  1. Position the new converter and secure it with the original hardware (or new if supplied).
  2. Tighten bolts to the manufacturer’s specifications (typically around 40 Nm).

4. Reconnect Components

• Reinstall the exhaust system components and ensure all connections are tight.
• Reconnect the oxygen sensor connectors.

5. Reset the Check Engine Light

• Reconnect the negative battery terminal.
• Use an OBD-II scanner to clear the P0420 code from the ECU.