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

Solution

1. Preparation

• Gather tools and parts required for the repair.
• Disconnect the battery (negative terminal) to prevent electrical shorts.
• Raise the vehicle securely on jack stands if needed.

2. Inspect and Replace Oxygen Sensors

1. Locate the oxygen sensors:
   • Identify the upstream (pre-catalytic converter) and downstream (post-catalytic converter) oxygen sensors.
2. Remove the sensors:
   • Use an O2 sensor socket to carefully unscrew the sensors from their harnesses.
3. Inspect the sensors:
   • Check for any signs of damage or contamination; replace if necessary.
4. Install new sensors:
   • Apply anti-seize compound to the threads of the new sensors.
   • Screw them into place and torque to manufacturer specifications (typically around 30-40 Nm).

3. Inspect and Replace Catalytic Converter

1. Check catalytic converter condition:
   • If the converter is damaged or clogged, it will need replacement.
2. Remove the exhaust system:
   • Unbolt the exhaust pipe from the catalytic converter and support it.
3. Remove the catalytic converter:
   • Unbolt the catalytic converter from its mounting brackets and exhaust flanges.
4. Install new catalytic converter:
   • Position the new catalytic converter, securing it with bolts and gaskets as needed.
   • Torque bolts to manufacturer specifications (typically around 25-30 Nm).
5. Reattach the exhaust system:
   • Ensure all connections are secure and no leaks are present.

4. Clear Codes and Test

1. Reconnect the battery.
2. Clear all error codes using the OBD-II scanner.
3. Test drive the vehicle for at least 20 minutes to ensure the check engine light does not reappear.