how to fix P0420 code on my BMW 5 Series G30/G31 (2017-2024)

Solution

1. Preparation

• Gather necessary tools and parts.
• Disconnect the battery to prevent electrical shock (negative terminal first).
• Raise the vehicle on jack stands for safe access to the exhaust system.

2. Inspect and Replace O2 Sensors

• Tools Required: O2 sensor socket, ratchet, torque wrench.
• Locate the upstream and downstream O2 sensors.
• Unscrew the upstream O2 sensor using an O2 sensor socket and replace it with a new one, tightening to manufacturer specifications (typically around 30 Nm).
• Repeat for the downstream O2 sensor if it was determined faulty.

3. Inspect and Replace the Catalytic Converter

• Tools Required: Socket set, torque wrench, exhaust gasket or sealant.
• Locate the catalytic converter in the exhaust system.
• Remove the bolts connecting the catalytic converter to the exhaust pipe and the front pipe, utilizing penetrating oil if necessary.
• Carefully detach the old catalytic converter and replace it with a new one, ensuring proper alignment.
• Reconnect the exhaust pipes and tighten bolts to the specified torque (typically around 40 Nm).

4. Reconnect Battery and Clear Codes

• Reconnect the negative battery terminal.
• Use the OBD-II scanner to clear the P0420 code from the system.