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

Solution

1. Preparation

• Gather tools and parts needed for the repair.
• Disconnect the battery to ensure safety while working on the vehicle.
• Ensure the vehicle is on a flat surface and secure it with wheel chocks.

2. Inspect Exhaust System

• Sub-steps:
  • Raise the vehicle using a hydraulic lift or jack stands.
  • Visually inspect the exhaust system from the manifold to the tailpipe for any signs of leaks or damage.
  • Tighten any loose connections and replace damaged components as needed.

3. Test Oxygen Sensors

• Sub-steps:
  • Reconnect the battery.
  • Start the engine and allow it to reach operating temperature.
  • Use a scan tool to monitor the upstream (pre-catalytic) and downstream (post-catalytic) oxygen sensor voltages.
  • If the downstream sensor is not responding correctly to changes in the upstream sensor, consider replacing it.

4. Catalytic Converter Inspection

• Sub-steps:
  • Use an infrared thermometer to measure the temperature before and after the catalytic converter.
  • A significant difference (typically over 100°F) indicates a clogged or inefficient catalytic converter.
  • If the converter is confirmed to be faulty, proceed to replace it.

5. Replace Catalytic Converter (if necessary)

• Sub-steps:
  • Remove any heat shields or protective covers if necessary.
  • Unbolt the catalytic converter from the exhaust system, noting any gaskets or O2 sensor connectors.
  • Install the new catalytic converter, ensuring all gaskets are replaced and connections are secure.
  • Torque the bolts to the manufacturer's specifications.