how to fix P0420 code on Toyota Highlander Third Generation (2014-2019)

Solution

1. Preparation

• Tools Required: OBD-II scanner, multimeter, socket set, jack and jack stands, safety glasses, gloves.
• Ensure the vehicle is parked on a level surface and the engine is cool.
• Disconnect the battery to prevent electrical shorts while working on the vehicle.

2. Inspect and Test Oxygen Sensors

• Sub-steps:
  1. Locate the upstream (pre-catalytic converter) and downstream (post-catalytic converter) oxygen sensors.
  2. Disconnect the electrical connectors from both oxygen sensors.
  3. Using a multimeter, set it to the voltage setting and measure the output of the upstream sensor (should fluctuate between 0.1V to 0.9V during operation).
  4. Repeat the measurement for the downstream sensor (should be less volatile compared to the upstream).

3. Replace Faulty Oxygen Sensors

• Sub-steps:
  1. If either sensor is faulty, remove it using an oxygen sensor socket.
  2. Apply anti-seize compound to the threads of the new sensor.
  3. Install the new sensor and tighten it to the manufacturer's specified torque (usually around 30 lb-ft).
  4. Reconnect the electrical connectors.

4. Inspect and Replace Catalytic Converter (if necessary)

• Sub-steps:
  1. If the catalytic converter is found to be damaged or clogged, support the exhaust system with a jack.
  2. Remove the bolts connecting the catalytic converter to the exhaust manifold and the exhaust pipe using a socket set.
  3. Carefully remove the old catalytic converter.
  4. Install the new catalytic converter, ensuring proper alignment.
  5. Tighten the bolts according to the manufacturer's torque specifications.

5. Clear Codes and Test Drive

• Sub-steps:
  1. Reconnect the battery.
  2. Use the OBD-II scanner to clear the P0420 code.
  3. Start the engine and let it reach operating temperature.
  4. Take the vehicle for a test drive to ensure the check engine light does not reappear.