how to fix P0420 code on my BMW 3 Series F30/F31 (2012-2019)

Solution

1. Preparation

• Gather tools and parts.
• Disconnect the battery before starting any work.
• Allow the exhaust system to cool down.

2. Inspect Oxygen Sensors

• Tools Required: OBD-II scanner, multimeter
• Remove the electrical connectors from both upstream and downstream oxygen sensors.
• Use the multimeter to measure the voltage output of the upstream sensor while the engine is running; it should fluctuate between 0.1V to 0.9V.
• Perform the same test on the downstream sensor; it should have a more stable output.

3. Examine the Catalytic Converter

• Tools Required: Exhaust thermometer, torque wrench
• Start the engine and allow it to reach operating temperature.
• Measure the temperature of the exhaust gas entering the catalytic converter and then the temperature of the gas exiting it. The exit temperature should be at least 100°F higher than the inlet temperature.
• If the converter does not meet this threshold, it may need to be replaced.

4. Replace Faulty Components

• Tools Required: Socket set, torque wrench, penetrating oil
• If an oxygen sensor is faulty, replace it:
  1. Apply penetrating oil to the sensor threads.
  2. Use the socket set to remove the faulty sensor.
  3. Install the new sensor and torque it to the manufacturer’s specifications.
• If the catalytic converter is deemed faulty, replace it:
  1. Disconnect any exhaust hangers or brackets holding the converter in place.
  2. Use the socket set to remove the bolts connecting the converter to the exhaust pipes.
  3. Install the new catalytic converter and torque the bolts to specifications.

5. Reconnect Components

• Reattach the oxygen sensor connectors.
• Reconnect the battery.