how to fix P0420 code in BMW 3 Series E90/E91 (2005-2012) related to the converter?

Solution

1. Preparation

• Tools Required: OBD-II scanner, multimeter, socket set, torque wrench, exhaust temperature probe.
• Safety Warnings: Allow the engine to cool before working on the exhaust system. Wear safety goggles and gloves.

2. Oxygen Sensor Inspection

• Disconnect the battery to prevent any electrical shorts.
• Locate the pre-catalytic and post-catalytic oxygen sensors.
• Remove the sensors using a socket wrench and inspect them for carbon buildup or damage.
• Clean the sensors with an appropriate cleaner or replace them if damaged.

3. Catalytic Converter Inspection

• Use a jack and jack stands to lift the vehicle safely.
• Remove the exhaust heat shield if applicable (typically requires a socket set).
• Inspect the catalytic converter for physical damage, such as cracks or holes.
• Measure the temperature at the inlet and outlet of the catalytic converter with an exhaust temperature probe.

4. Catalytic Converter Replacement (if necessary)

• If the catalytic converter is found to be faulty, proceed with replacement.
  1. Remove the exhaust pipe bolts and any clamps securing the catalytic converter.
  2. Detach the catalytic converter from the exhaust system.
  3. Install the new catalytic converter and secure it with bolts and clamps, ensuring proper alignment.
  4. Torque bolts to manufacturer specifications (typically around 30-40 Nm, but check the service manual for exact values).

5. Reassemble and Reconnect

• Reinstall the oxygen sensors and torque them to specifications.
• Reattach the exhaust heat shield if it was removed.
• Reconnect the battery and clear the error codes using the OBD-II scanner.