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

Solution

1. Preparation

• Gather necessary tools and parts.
• Disconnect the vehicle's battery to ensure safety.
• Allow the exhaust system to cool down before working.

2. Inspect and Test Oxygen Sensors

• Tools Required: OBD-II scanner, multimeter.
• Remove the upstream and downstream oxygen sensors using a socket set.
• Connect the multimeter to the oxygen sensor connector and check the voltage output.
  • Expected Voltage: 0.1 to 0.9 volts for a functioning sensor.
• If the voltage readings are outside this range, replace the faulty oxygen sensor.

3. Check Catalytic Converter

• Tools Required: Jack and jack stands, exhaust pipe cutter (if necessary).
• Inspect the catalytic converter for any physical damage, such as dents or rust.
• If the converter is clogged, use a vacuum gauge to check back pressure.
  • Acceptable Back Pressure: Below 1.5 psi at idle.
• If back pressure is higher, it may need replacement.

4. Replace Catalytic Converter (if necessary)

• Tools Required: Socket set, exhaust pipe cutter, gasket scraper.
• Disconnect the exhaust pipe from the catalytic converter using the exhaust pipe cutter if necessary.
• Remove the catalytic converter by unbolting it from the exhaust manifold and the exhaust pipe.
• Install the new catalytic converter with new gaskets, ensuring a proper seal. Torque bolts to manufacturer specifications (typically around 30 Nm).
• Reconnect the exhaust pipe.

5. Reinstall Oxygen Sensors

• Reinstall the upstream and downstream oxygen sensors, tightening them to manufacturer specifications (usually around 30 Nm).
• Reconnect the vehicle's battery.