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

Solution

1. Preparation

• Gather tools and parts.
• Disconnect the negative battery terminal to prevent electrical shorts.
• Allow the vehicle to cool down before starting work.

2. Inspect and Replace Oxygen Sensors

1. Remove the upstream oxygen sensor:
   • Use an oxygen sensor socket to unscrew the sensor from the exhaust manifold.
   • Disconnect the electrical connector.
2. Install the new upstream oxygen sensor:
   • Apply anti-seize compound to the threads (if required).
   • Torque the sensor to manufacturer specifications (typically around 30 Nm).
   • Reconnect the electrical connector.
3. Remove the downstream oxygen sensor:
   • Repeat the process for the downstream sensor located after the catalytic converter.
4. Install the new downstream oxygen sensor:
   • Similar to the upstream, apply anti-seize and torque accordingly.

3. Inspect and Replace the Catalytic Converter

1. Remove exhaust components:
   • Unbolt any necessary exhaust parts to access the catalytic converter.
   • Use a socket set for the bolts and carefully support the exhaust system.
2. Remove the catalytic converter:
   • Disconnect any mounting brackets or bolts securing the catalytic converter.
   • Carefully remove the old catalytic converter.
3. Install the new catalytic converter:
   • Position the new catalytic converter and secure it with the mounting hardware.
   • Ensure all gaskets are replaced and sealed properly.
4. Reassemble exhaust components:
   • Bolt back any removed exhaust parts and check for proper alignment.

4. Final Checks

• Reconnect the negative battery terminal.
• Start the engine and allow it to reach operating temperature.
• Clear the P0420 code using the OBD-II scanner.