why does my Toyota Corolla E210 (2019-2024) keep throwing P0420 code?

Solution

1. Preparation

• Gather necessary tools and safety equipment.
• Disconnect the negative battery terminal to avoid electrical shorts.

2. Oxygen Sensor Replacement (if faulty)

• Tools Required: O2 sensor socket, ratchet, torque wrench
• Remove the upstream and/or downstream oxygen sensors based on diagnostic results.
  1. Locate the oxygen sensor(s) connected to the exhaust system.
  2. Use the O2 sensor socket to unscrew the sensor from the exhaust pipe or catalytic converter.
  3. Install the new sensor and torque it to manufacturer's specification (typically around 30 ft-lbs).

3. Catalytic Converter Replacement (if necessary)

• Tools Required: Socket set, torque wrench, exhaust pipe cutter (if required), gasket scraper
• If the catalytic converter is confirmed to be faulty, follow these steps:
  1. Remove the exhaust heat shield (if applicable) by unscrewing the bolts.
  2. Disconnect the exhaust pipes connected to the catalytic converter, using a socket set.
  3. Remove any hangers or supports holding the catalytic converter in place.
  4. Install the new catalytic converter, ensuring gaskets are replaced and the bolts are torqued to specification (usually around 30-40 ft-lbs).

4. Final Checks

• Reconnect all components and ensure there are no leaks in the exhaust system.
• Reconnect the negative battery terminal.
• Start the engine and let it idle for a few minutes to ensure everything is functioning properly.