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

Solution

1. Preparation

• Gather all necessary tools and parts.
• Ensure the vehicle is parked on a level surface, and the engine is cooled down.
• Disconnect the battery to prevent electrical shorts.

2. Inspect and Replace Oxygen Sensors

• Tools Required: O2 sensor socket, wrench, multimeter.
• Sub-steps:
  1. Locate the upstream (pre-catalytic) and downstream (post-catalytic) oxygen sensors.
  2. Disconnect the electrical connectors from both sensors.
  3. Use the O2 sensor socket to remove the upstream sensor. If it’s seized, apply penetrating oil and allow it to soak before attempting removal.
  4. Install the new upstream O2 sensor and torque it to the manufacturer's specification (typically around 30 lb-ft).
  5. Repeat the removal and installation process for the downstream O2 sensor.
  6. Reconnect the electrical connectors for both sensors.

3. Inspect and Replace Catalytic Converter (if necessary)

• Tools Required: Socket set, torque wrench, exhaust hanger removal tool.
• Sub-steps:
  1. Raise the vehicle safely on jack stands or a lift.
  2. Inspect the catalytic converter for any physical damage or excessive carbon build-up.
  3. Remove any heat shields or brackets securing the catalytic converter.
  4. Use the socket set to detach the exhaust pipes connected to the catalytic converter.
  5. Remove the catalytic converter from its mounting location.
  6. Install the new catalytic converter, ensuring it is properly aligned.
  7. Reattach exhaust pipes and torque them to manufacturer specifications.
  8. Reinstall any heat shields or brackets.

4. Clear Codes and Test Drive

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