how to fix P0420 code on BMW 5 Series G30/G31 (2017-2024)

Solution

1. Preparation

• Tools Required: OBD-II scanner, multimeter, jack and jack stands, socket set, torque wrench, safety glasses, gloves.
• Allow the vehicle to cool down before starting work.
• Disconnect the battery to avoid electrical shorts.

2. Inspect and Replace Oxygen Sensors (if faulty)

• Sub-steps:
  1. Locate the upstream and downstream oxygen sensors connected to the exhaust system.
  2. Disconnect the electrical connectors from both sensors.
  3. Use a socket wrench to remove the sensors from their mounting locations.
  4. Install new oxygen sensors, ensuring they are tightened to the manufacturer’s torque specification (typically around 30 Nm).
  5. Reconnect the electrical connectors securely.

3. Check and Replace the Catalytic Converter (if damaged)

• Sub-steps:
  1. Support the vehicle on jack stands and remove the underbody panels if present.
  2. Disconnect the exhaust pipes at the flanges using a socket wrench.
  3. Remove any mounting brackets and heat shields obstructing access to the catalytic converter.
  4. Carefully remove the old catalytic converter.
  5. Install the new catalytic converter, ensuring proper alignment and sealing.
  6. Reattach the exhaust pipes and secure all mounting brackets, torquing to manufacturer specifications.

4. Clear Codes and Test Drive

• Sub-steps:
  1. Reconnect the battery.
  2. Use the OBD-II scanner to clear the P0420 code.
  3. Start the engine and let it idle for a few minutes.
  4. Take the vehicle for a test drive to ensure that the check engine light does not reappear.