why is my Toyota Highlander Third Generation (2014-2019) check engine light on with code P0420?

Solution

1. Preparation

• Gather tools and materials necessary for the repair.
• Disconnect the battery to ensure safety while working on the vehicle.

2. Inspect Oxygen Sensors

• Locate the upstream (pre-catalytic) and downstream (post-catalytic) oxygen sensors.
• Remove the connectors and use a multimeter to test the voltage output of the sensors.
  • Upstream Sensor: Should fluctuate between 0.1V and 0.9V.
  • Downstream Sensor: Should show a stable voltage if the catalytic converter is functioning properly.
• If the upstream sensor is faulty, replace it.

3. Inspect and Replace Catalytic Converter

• If oxygen sensor tests are satisfactory, inspect the catalytic converter.
• Remove the exhaust components as necessary to access the catalytic converter.
• If damaged or clogged, replace the catalytic converter with a new OEM or high-quality aftermarket part.
• Ensure all gaskets and seals are replaced to prevent leaks.

4. Reconnect Battery and Clear Codes

• Reconnect the battery terminals securely.
• Use the OBD-II scanner to clear the P0420 code from the vehicle’s computer.

5. Test Drive

• Start the engine and allow it to reach operating temperature.
• Test drive the vehicle under various conditions to ensure that the check engine light does not reappear.