how do I fix the P0420 code in my BMW 5 Series G30/G31 (2017-2024)

Solution

1. Preparation

• Gather tools and parts needed.
• Ensure the vehicle is parked on a flat surface and the engine is off and cool.
• Disconnect the battery to prevent any electrical shorts.

2. Inspect and Replace O2 Sensors (if faulty)

• 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 sensor(s).
  3. Install the new oxygen sensor(s) and torque to the manufacturer's specifications (typically around 30 lb-ft).
  4. Reconnect the electrical connectors securely.

3. Inspect and Replace Catalytic Converter (if necessary)

• Sub-steps:
  1. Support the vehicle on jack stands and remove the exhaust heat shield if necessary.
  2. Use a socket set to unbolt the catalytic converter from both the exhaust manifold and the exhaust pipe.
  3. Remove the old catalytic converter and inspect the flange and gaskets for damage.
  4. Install the new catalytic converter and torque the bolts to the manufacturer’s specifications (typically around 30 lb-ft for flanges).
  5. Replace the exhaust gaskets with new ones to ensure a proper seal.

4. Clear Trouble Codes

• Sub-steps:
  1. Reconnect the battery.
  2. Use the OBD-II scanner to clear the P0420 code from the vehicle’s computer.

5. Final Inspection

• Sub-steps:
  1. Start the engine and allow it to reach operating temperature.
  2. Inspect for exhaust leaks and ensure all connections are secure.