how to fix P0420 code on my Toyota Highlander Fourth Generation (2020-present)

Solution

1. Preparation

• Gather tools and parts.
• Disconnect the negative battery terminal to prevent electrical shorts.
• Allow the vehicle to cool down completely before working on the exhaust system.

2. Inspect and Test Oxygen Sensors

• Tools Required: OBD-II scanner, multimeter
• Check the operation of the upstream (pre-catalytic) oxygen sensor:
  • Reconnect the battery and start the engine.
  • Use the OBD-II scanner to monitor the voltage output; it should fluctuate between 0.1V and 0.9V.
• If faulty, replace the upstream oxygen sensor.

3. Replace the Catalytic Converter (if necessary)

• Tools Required: Socket set, torque wrench, penetrating oil, gasket scraper
• Steps:
  1. Raise the vehicle securely on jack stands.
  2. Apply penetrating oil to the bolts securing the catalytic converter to the exhaust manifold and exhaust pipe.
  3. Remove the bolts and disconnect the catalytic converter.
  4. Clean the mating surfaces on the exhaust manifold and exhaust pipe with a gasket scraper.
  5. Install the new catalytic converter, ensuring proper alignment.
  6. Torque the bolts to manufacturer specifications (typically around 25-30 ft-lbs).

4. Replace Downstream Oxygen Sensor (if necessary)

• If the downstream oxygen sensor is also faulty, proceed to replace it:
  1. Disconnect the electrical connector from the sensor.
  2. Unscrew the sensor using a suitable socket.
  3. Install the new sensor and reconnect the electrical connector.

5. Final Steps

• Reconnect the negative battery terminal.
• Start the engine and let it idle for a few minutes to ensure everything is functioning correctly.