how do I fix the P0420 code on my BMW 3 Series G20/G21 (2019-2024)?

Solution

1. Preparation

• Gather necessary tools and parts.
• Disconnect the battery to ensure safety during repair.
• Allow the exhaust system to cool before working on it.

2. Inspect and Replace Oxygen Sensors (if faulty)

• Tools Required: O2 sensor socket, ratchet, torque wrench, multimeter.
• Sub-steps:
  1. Locate the upstream and downstream oxygen sensors on the exhaust manifold and catalytic converter.
  2. Use an O2 sensor socket to remove the faulty oxygen sensor(s).
  3. Install the new oxygen sensor(s) and torque to manufacturer's specifications (typically around 30 Nm).
  4. Reconnect the battery.

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

• Tools Required: Socket set, torque wrench, exhaust gasket sealant.
• Sub-steps:
  1. Remove the exhaust heat shield if applicable.
  2. Detach the exhaust pipes connected to the catalytic converter using a socket set.
  3. Remove the catalytic converter from the vehicle.
  4. Install the new catalytic converter and ensure proper alignment.
  5. Reconnect the exhaust pipes and torque to specifications (usually around 40 Nm).
  6. Apply exhaust gasket sealant if needed to prevent leaks.