how to fix P0420 code in BMW 3 Series G20/G21 (2019-2024)

Solution

1. Preparation

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

2. Inspect and Replace Oxygen Sensors

1. Locate the Sensors

   • Identify the upstream (pre-catalytic) and downstream (post-catalytic) oxygen sensors.

2. Remove the Sensors

   • Use an oxygen sensor socket to carefully unscrew the sensors from their respective locations.
   • Disconnect the wiring harness from each sensor.

3. Install New Sensors

   • Apply anti-seize lubricant to the threads of the new sensors.
   • Screw in the new sensors and reconnect the wiring harnesses. Torque to manufacturer specifications (typically around 30 Nm).

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

1. Remove Exhaust Components

   • Use a socket set to detach any bolts securing the exhaust system, including the catalytic converter.
   • Carefully lower or remove the exhaust components to gain access to the catalytic converter.

2. Inspect the Catalytic Converter

   • Check for signs of damage, clogging, or contamination.

3. Install New Catalytic Converter

   • Position the new catalytic converter into place.
   • Reattach exhaust components and torque bolts to manufacturer specifications (typically around 40 Nm).
   • Ensure all gaskets are replaced and seals are tight to prevent exhaust leaks.

4. Reconnect Battery and Clear Codes

• Reconnect the battery terminals.
• Use the OBD-II scanner to clear the P0420 code from the ECM.