my BMW 5 Series G30/G31 (2017-2024) has a P0420 code, what does it indicate?

Solution

1. Preparation

• Gather all necessary tools and parts.
• Disconnect the battery to prevent electrical shorts.
• Allow the vehicle to cool down to avoid burns.

2. Inspect and Test Oxygen Sensors

• Tools Required: OBD-II scanner, multimeter.
• Remove the oxygen sensors from the exhaust system.
• Use the multimeter to test the voltage output of both the pre-catalytic and post-catalytic oxygen sensors.
  • Expected values: Pre-catalytic should fluctuate between 0.1 to 0.9 volts; Post-catalytic should be relatively stable (0.1-0.5 volts).
• If either sensor is faulty, replace it.

3. Inspect and Replace Catalytic Converter (if necessary)

• Tools Required: Socket set, torque wrench, exhaust pipe cutter (if needed).
• Remove the exhaust system components attached to the catalytic converter.
• Cut and remove the old catalytic converter from the exhaust system if it is blocked or damaged.
• Install the new catalytic converter, ensuring all gaskets are replaced and connections are secure.
• Torque the bolts to the manufacturer's specifications (refer to repair manual for specific torque values).

4. Reassemble Exhaust System

• Reattach any remaining exhaust components.
• Ensure all hangers and mounts are secure.
• Reconnect any sensors that were disconnected during the process.

5. Clear Codes and Test Drive

• Tools Required: OBD-II scanner.
• Reconnect the battery.
• Use the OBD-II scanner to clear the P0420 code.
• Test drive the vehicle under various conditions to ensure the check engine light does not reappear.