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

Solution

1. Preparation

• Gather necessary tools and parts.
• Ensure the vehicle is parked on a level surface and the engine is cool.
• Disconnect the negative battery terminal to prevent electrical shorts.

2. Inspect and Replace Oxygen Sensors

• Tools Required: O2 sensor socket, torque wrench, penetrating oil.
• Identify the upstream and downstream oxygen sensors.
• Apply penetrating oil to the sensor threads and allow it to soak.
• Use the O2 sensor socket to remove the upstream oxygen sensor.
• Install the new sensor, ensuring it is torqued to the manufacturer's specification (usually around 30 Nm or 22 ft-lb).
• Repeat for the downstream oxygen sensor if necessary.

3. Inspect and Replace Catalytic Converter

• Tools Required: Socket set, jack and jack stands, exhaust gasket.
• Raise the vehicle and secure it with jack stands.
• Disconnect the exhaust pipe from the catalytic converter by removing the bolts.
• Remove any support brackets or heat shields that may obstruct the catalytic converter.
• Remove the catalytic converter from the exhaust manifold.
• Install the new catalytic converter, ensuring proper alignment and securing it with new gaskets and bolts.
• Connect the exhaust pipe back to the catalytic converter.

4. Reconnect Battery and Reset Code

• Reconnect the negative battery terminal.
• Use the OBD-II scanner to clear the P0420 code from the engine control module.
• Start the engine and allow it to reach operating temperature.