how to fix P0420 code on BMW 3 Series G20/G21 (2019-2024)

Solution

1. Preparation

• Gather tools and parts required for the repair.
• Disconnect the battery to prevent any electrical shorts.
• Ensure the vehicle is on a flat surface and lift it safely using jack stands.

2. Inspect and Replace Oxygen Sensors (if necessary)

• Tools Required: O2 sensor socket, wrench set, multimeter
• Remove the upstream oxygen sensor:
  1. Locate the upstream O2 sensor near the engine.
  2. Use the O2 sensor socket to unscrew the sensor.
• Install the new upstream O2 sensor:
  1. Apply anti-seize compound to the threads (if applicable).
  2. Torque to manufacturer specifications (usually around 30 Nm).
• Repeat for the downstream O2 sensor if it is also faulty.

3. Inspect and Replace Catalytic Converter (if necessary)

• Tools Required: Wrench set, socket set, exhaust hanger removal tool
• Remove the catalytic converter:
  1. Disconnect any bolts connecting the exhaust pipe to the catalytic converter.
  2. Remove any exhaust hangers holding the catalytic converter in place.
  3. Carefully detach the catalytic converter from the exhaust system.
• Install the new catalytic converter:
  1. Position the new catalytic converter in place.
  2. Connect it to the exhaust pipe and secure it with bolts.
  3. Reattach exhaust hangers ensuring proper alignment.

4. Reconnect Battery and Clear Codes

• Reconnect the battery terminals.
• Use the OBD-II scanner to clear the P0420 code and any other related codes.