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

Solution

1. Preparation

• Gather necessary tools and parts.
• Disconnect the negative battery terminal to prevent electrical shorts.
• Allow the exhaust system to cool before working on it to prevent burns.

2. Replace Oxygen Sensors (if faulty)

• Tools Required: O2 sensor socket, ratchet, torque wrench, penetrating oil.
• Sub-steps:
  1. Locate the upstream (pre-catalytic converter) and downstream (post-catalytic converter) oxygen sensors.
  2. Apply penetrating oil to the sensor threads if they are rusted or corroded.
  3. Disconnect the electrical connectors from both oxygen sensors.
  4. Use the O2 sensor socket to remove the sensors from the exhaust manifold and catalytic converter.
  5. Install new oxygen sensors by reversing the removal steps and torque to the manufacturer's specifications (typically around 30 lb-ft).

3. Inspect and Clean or Replace Catalytic Converter

• Tools Required: Wrench set, jack stands, exhaust pipe cutter (if necessary).
• Sub-steps:
  1. If no physical damage is found, check for internal blockage; if necessary, remove the catalytic converter.
  2. Use an exhaust pipe cutter to sever the pipe if it's welded.
  3. Inspect the converter for any signs of damage. If blocked or damaged, replace it with a new unit.
  4. Install the new catalytic converter, ensuring proper alignment and sealing.
  5. Reattach any exhaust components and secure with appropriate hardware.

4. Clear Error Codes

• Tools Required: OBD-II scanner.
• Sub-steps:
  1. Reconnect the negative battery terminal.
  2. Use the OBD-II scanner to clear the P0420 code from the vehicle’s computer.