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

Solution

1. Preparation

• Gather necessary tools and parts.
• Disconnect the battery to prevent electrical shorts.
• Ensure the vehicle is securely raised on jack stands if working underneath.

2. Inspect and Replace Oxygen Sensors

1. Locate the upstream (pre-catalytic) and downstream (post-catalytic) oxygen sensors.
2. Use a socket wrench to carefully unscrew the oxygen sensors from their respective locations.
3. Inspect the sensors for damage; if they are faulty, replace them with new ones.
4. Apply anti-seize compound to the threads of the new oxygen sensors.
5. Install the new sensors and torque to manufacturer specifications (typically around 30 Nm).

3. Inspect and Replace the Catalytic Converter

1. If the catalytic converter is damaged or clogged, proceed to remove it.
2. Remove any heat shields or exhaust hangers obstructing access to the catalytic converter.
3. Use a reciprocating saw or exhaust cut-off tool to carefully cut the exhaust pipes at both ends of the catalytic converter if it is welded in place.
4. Install a new catalytic converter by reversing the removal process, ensuring all connections are secure.
5. Tighten the exhaust clamps to manufacturer specifications (usually around 25 Nm).

4. Reconnect Battery and Reset Codes

1. Reconnect the battery terminals.
2. Use the OBD-II scanner to clear the P0420 code from the vehicle’s memory.