how to fix P0420 code on my Toyota Highlander XU70 (2020-Present)

Solution

1. Preparation

• Gather all necessary tools and parts.
• Disconnect the negative battery terminal to prevent electrical shock.
• Allow the engine to cool completely before working on the exhaust system.

2. Inspect Oxygen Sensors

• Tools Required: O2 sensor socket, multimeter
  • Remove the downstream oxygen sensor using the O2 sensor socket.
  • Test the sensor's resistance and voltage output using a multimeter.
  • Replace the sensor if it is out of specification.

3. Check Catalytic Converter

• Tools Required: Infrared thermometer
  • Start the engine and allow it to reach operating temperature.
  • Measure the temperature at the inlet of the catalytic converter and then at the outlet.
  • The outlet temperature should be significantly higher than the inlet (typically a difference of 100-200°F). If not, the catalytic converter may need replacement.

4. Replace Catalytic Converter (if necessary)

• Tools Required: Socket set, torque wrench, exhaust gasket
  • Raise the vehicle securely on jack stands.
  • Remove any heat shields or brackets obstructing access to the catalytic converter.
  • Unbolt the catalytic converter from the exhaust manifold and the exhaust pipe.
  • Install the new catalytic converter with a new gasket, ensuring proper alignment and torque specifications (typically 30-40 ft-lbs depending on the model).
  • Reinstall any removed components.

5. Reinstall Oxygen Sensors

• Reinstall the downstream oxygen sensor back into the catalytic converter.
• Reconnect the negative battery terminal.