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

Solution

1. Preparation

• Gather necessary tools and parts.
• Ensure the vehicle is parked on a flat surface and the engine is cool.
• Disconnect the negative battery terminal to prevent electrical shorts.

2. Inspect and Repair Exhaust Leaks

• Sub-steps:
  1. Use a flashlight to inspect the exhaust system for cracks or holes.
  2. Repair any leaks found using exhaust tape or replace damaged sections of the exhaust pipe.
  3. Reconnect the battery terminal once repairs are made.

3. Test and Replace Oxygen Sensors

• Sub-steps:
  1. Identify the upstream (pre-catalytic) and downstream (post-catalytic) oxygen sensors.
  2. Disconnect the electrical connectors from the sensors.
  3. Use a multimeter to test the voltage output of the sensors (should fluctuate between 0.1V - 0.9V for the upstream sensor).
  4. If the upstream sensor is faulty, replace it with a new sensor.
  5. If the downstream sensor is faulty, replace it as well.

4. Replace the Catalytic Converter (if necessary)

• Sub-steps:
  1. Remove any heat shields or brackets securing the catalytic converter.
  2. Use a socket set to unbolt the catalytic converter from the exhaust system.
  3. Install the new catalytic converter, ensuring proper alignment and secure with bolts to manufacturer specifications (usually around 25-30 ft-lbs).
  4. Reinstall heat shields and brackets.

5. Clear Codes and Test Drive

• Sub-steps:
  1. Reconnect the negative battery terminal.
  2. Use an OBD-II scanner to clear the P0420 code from the PCM.
  3. Start the vehicle and perform a test drive to ensure the engine operates smoothly and the check engine light remains off.