how to fix the P0420 code on my BMW 5 Series F10/F11 (2010-2017)

Solution

1. Preparation

• Gather tools and parts required for the repair.
• Ensure the vehicle is parked on a level surface and secure it with wheel chocks.
• Disconnect the negative battery terminal to prevent any electrical issues.

2. Inspect Oxygen Sensors

• Tools Required: OBD-II scanner, multimeter
• Remove the upstream (pre-catalytic) oxygen sensor using a socket wrench.
• Test the sensor with a multimeter to check its voltage output (should fluctuate between 0.1V and 0.9V).
• If the sensor is faulty, replace it with a new one.

3. Replace Catalytic Converter (if necessary)

• Tools Required: Socket set, torque wrench, exhaust pipe cutter (if applicable)
• Raise the vehicle using a jack and secure it with jack stands.
• Remove the heat shield if present, using a socket set.
• Disconnect the exhaust pipes from the catalytic converter; cut the pipes if they are welded.
• Remove the catalytic converter by unbolting it from the exhaust manifold and the mid-pipe.
• Install the new catalytic converter by reversing the removal steps, ensuring all bolts are torqued to the manufacturer's specifications.

4. Reinstall Oxygen Sensors

• Reinstall the upstream oxygen sensor into the new catalytic converter, ensuring it is secured properly.
• If the downstream (post-catalytic) oxygen sensor was removed, reinstall it as well.

5. Final Checks

• Reconnect the negative battery terminal.
• Start the engine and let it idle for a few minutes to check for leaks.
• Clear the P0420 code using the OBD-II scanner.