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

Solution

1. Preparation

• Gather necessary tools and parts.
• Disconnect the battery to ensure safety during repairs.
• Allow the engine to cool down before working on the exhaust system.

2. Inspect and Test Oxygen Sensors

• Tools Required: OBD-II scanner, multimeter
• Remove the upstream and downstream oxygen sensor connectors.
• Use the multimeter to check the voltage output; it should fluctuate between 0.1V and 0.9V for the upstream sensor. If it does not, replace the sensor.
• If the downstream sensor is not functioning properly, replace it as well.

3. Inspect and Replace Catalytic Converter (if necessary)

• Tools Required: Socket set, exhaust pipe cutters, torque wrench
• Remove any heat shields covering the catalytic converter.
• Using the socket set, disconnect the exhaust pipes from the catalytic converter. You may need to cut the pipes if they are rusted together.
• Remove the old catalytic converter from the vehicle and inspect the flanges for any damage.
• Install the new catalytic converter, ensuring it is aligned properly with the exhaust system.
• Torque the bolts to the manufacturer's specifications (usually around 30-40 Nm, but verify for your specific part).

4. Clear Codes and Test Drive

• Reconnect the battery and use the OBD-II scanner to clear the P0420 code.
• Start the engine and let it run for a few minutes. Then, take the vehicle for a test drive to ensure that the check engine light does not reappear.