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

Solution

1. Preparation

• Gather necessary tools and parts.
• Disconnect the negative battery terminal.
• Allow the engine to cool before starting work.

2. Inspect and Replace Oxygen Sensors

• Tools Required: O2 sensor socket, socket wrench, anti-seize compound.
• Sub-steps:
  1. Locate the upstream (pre-catalytic) and downstream (post-catalytic) oxygen sensors.
  2. Use the O2 sensor socket to remove the upstream sensor.
  3. Install the new sensor after applying anti-seize compound to the threads.
  4. Repeat for the downstream sensor.
  5. Reconnect the battery terminal.

3. Inspect and Replace Catalytic Converter (if necessary)

• Tools Required: Jack and jack stands, socket set, exhaust hanger removal tool, gasket scraper.
• Sub-steps:
  1. Lift the vehicle using a jack and secure it with jack stands.
  2. Remove any exhaust hangers and bolts securing the catalytic converter.
  3. Carefully take out the catalytic converter from the exhaust system.
  4. Clean the mounting surfaces on the exhaust pipes to ensure a good seal for the new catalytic converter.
  5. Install the new catalytic converter, securing it with bolts and hangers.
  6. Reconnect any oxygen sensors that were disconnected.

4. Recheck System

• Start the engine and allow it to reach operating temperature.
• Check for any exhaust leaks around the catalytic converter and O2 sensors.