how to fix BMW 3 Series E90/E91 (2005-2012) P0420 code

Solution

1. Preparation

• Gather necessary tools and parts.
• Disconnect the battery to ensure safety while working on the vehicle.
• Allow the vehicle to cool down before handling exhaust components.

2. Check and Replace Oxygen Sensors (if faulty)

• Tools Required: O2 sensor socket, ratchet and extension, torque wrench
• Locate the pre-catalytic converter oxygen sensor and disconnect the wiring harness.
• Use the O2 sensor socket to remove the old sensor from the exhaust pipe.
• Install the new oxygen sensor and torque it to the manufacturer's specification (usually around 30 Nm).
• Reconnect the wiring harness.

3. Inspect and Replace the Catalytic Converter (if necessary)

• Tools Required: Socket set, penetrating oil, exhaust pipe cutter (if needed), new gaskets
• Remove the exhaust heat shield (if applicable) to access the catalytic converter.
• Apply penetrating oil to the bolts securing the catalytic converter and allow it to sit for a few minutes.
• Use a socket set to remove the bolts and disconnect the catalytic converter from the exhaust system.
• Install the new catalytic converter, ensuring to replace any gaskets and torque the bolts to specification.
• Reinstall the heat shield if it was removed.

4. Clear Codes and Test Drive

• Reconnect the battery.
• Use the OBD-II scanner to clear the P0420 code from the vehicle’s computer.
• Start the engine and allow it to warm up.
• Perform a test drive to ensure the code does not return and check for any abnormal symptoms.