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 (negative terminal) to avoid any electrical shorts.
• Raise the vehicle securely using jack stands.

2. Inspect and Replace Oxygen Sensors

1. Locate the upstream and downstream oxygen sensors.
2. Use an O2 sensor socket to remove the upstream sensor.
3. Install the new upstream oxygen sensor and torque to manufacturer's specifications (typically around 30 Nm).
4. Repeat the process for the downstream oxygen sensor if it is faulty.

3. Inspect and Replace Catalytic Converter (if necessary)

1. Remove any heat shields or brackets securing the catalytic converter.
2. Unbolt the catalytic converter from the exhaust system using a socket set (common sizes: 13mm or 15mm).
3. Inspect the old catalytic converter for damage or clogging.
4. Install the new catalytic converter and torque the bolts to specifications (usually around 50 Nm).
5. Reinstall any heat shields or brackets removed earlier.

4. Clear Engine Codes

1. Reconnect the battery.
2. Use the OBD-II scanner to clear the P0420 code from the ECM.
3. Start the engine and allow it to reach operating temperature.