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

Solution

1. Preparation

• Gather necessary tools and parts.
• Disconnect the negative battery terminal to prevent electrical shorts.
• Allow the vehicle to cool down if it has been running recently.

2. Inspect Exhaust System

• Visually check for cracks or holes in the exhaust pipes and catalytic converter.
• Use a smoke machine or soapy water to identify any leaks.
• Repair any leaks found using exhaust tape or replace damaged components.

3. Test Oxygen Sensors

• Locate the upstream (pre-catalytic converter) and downstream (post-catalytic converter) oxygen sensors.
• Disconnect the sensors and use a multimeter to check the voltage output:
  • Upstream should fluctuate between 0.1 to 0.9 volts rapidly while the engine is running.
  • Downstream should remain relatively steady.
• If either sensor is faulty, replace it.

4. Replace Catalytic Converter (if necessary)

• If the catalytic converter is confirmed faulty, unbolt the exhaust flanges on both sides of the converter.
• Remove the old catalytic converter and clean the mating surfaces on the exhaust pipes.
• Install the new catalytic converter, ensuring proper alignment.
• Torque the bolts to the manufacturer’s specifications (typically around 30-40 ft-lbs).

5. Reconnect and Test

• Reconnect the oxygen sensors and the negative battery terminal.
• Start the engine and allow it to reach normal operating temperature.
• Clear the trouble codes using the OBD-II scanner and take the vehicle for a test drive.