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

Solution

1. Preparation

• Gather tools and parts required.
• Ensure the vehicle is parked on a level surface and the engine is cool.
• Disconnect the battery to avoid electrical shorts.

2. Inspect and Replace Oxygen Sensors

• Tools Required: O2 sensor socket, ratchet, torque wrench.
• Sub-steps:
  1. Locate the upstream and downstream oxygen sensors.
  2. Remove the electrical connectors from both sensors.
  3. Unscrew the sensors using the O2 sensor socket.
  4. Install the new sensors and torque to manufacturer specifications (typically around 30 Nm).
  5. Reconnect the electrical connectors.

3. Inspect and Replace Catalytic Converter

• Tools Required: Socket set, cutting tool (if necessary for welded converters), sealant, torque wrench.
• Sub-steps:
  1. Locate the catalytic converter and inspect for physical damage.
  2. If damaged, remove the exhaust pipes connected to the catalytic converter.
  3. Use a cutting tool if the converter is welded in place.
  4. Install the new catalytic converter and secure it using bolts and sealant if required.
  5. Torque the bolts according to manufacturer specifications.

4. Clear Codes and Test

• Tools Required: OBD-II scanner.
• Sub-steps:
  1. Reconnect the battery.
  2. Use the OBD-II scanner to clear the P0420 code.
  3. Start the engine and let it run until it reaches operating temperature.
  4. Perform a test drive to ensure the code does not return.