how to fix P0420 in my BMW 5 Series F10/F11 (2010-2017) and pass emissions test

Solution

1. Preparation

• Gather necessary tools and parts.
• Disconnect the battery to ensure safety.
• Raise the vehicle and secure it on jack stands.

2. Inspect and Replace Oxygen Sensors

• Tools Required: O2 sensor socket, torque wrench
• Remove the upstream (pre-catalytic) oxygen sensor using the O2 sensor socket.
• Install the new oxygen sensor and torque to manufacturer specifications (typically 30 Nm).
• Repeat for the downstream (post-catalytic) oxygen sensor if it is also faulty.

3. Inspect and Replace Catalytic Converter

• Tools Required: Socket set, exhaust pipe cutter, torch, gasket scraper
• Remove any heat shields or brackets securing the catalytic converter.
• Cut the exhaust pipe before and after the catalytic converter using an exhaust pipe cutter.
• Remove the old catalytic converter and clean the mating surfaces.
• Install the new catalytic converter, securing it with new gaskets and torquing bolts to manufacturer specifications (usually around 40 Nm).
• Reattach any heat shields or brackets.

4. Clear Codes and Test

• Reconnect the battery and use the OBD-II scanner to clear the P0420 code.
• Start the engine and allow it to reach operating temperature.
• Monitor the system for any reoccurring check engine light.