how to fix the P0420 code on my Toyota Highlander Fourth Generation (2020-present)

Solution

1. Preparation

• Tools Required: OBD-II scanner, multimeter, socket set, torque wrench, exhaust backpressure gauge.
• Safety Warnings: Disconnect the battery before working on electrical systems. Allow the engine to cool before inspecting the exhaust system.

2. Address any Faulty Oxygen Sensors

• Sub-steps:
  1. Locate the upstream (pre-catalytic converter) and downstream (post-catalytic converter) oxygen sensors.
  2. Disconnect the electrical connectors from both oxygen sensors.
  3. Remove the sensors using a socket wrench.
  4. Inspect the sensors for damage; replace if faulty.
  5. Install new oxygen sensors and torque to manufacturer specifications (typically around 30 lb-ft).

3. Repair or Replace the Catalytic Converter

• Sub-steps:
  1. If the catalytic converter is found to be faulty, remove the exhaust pipes connected to it, using a socket set.
  2. If applicable, remove any heat shields obstructing access to the catalytic converter.
  3. Disconnect the catalytic converter from the exhaust system and remove it from the vehicle.
  4. Install the new catalytic converter, ensuring all gaskets are replaced and the unit is properly aligned.
  5. Reconnect the exhaust pipes and torque bolts to manufacturer specifications.

4. Clear the Codes

• Sub-steps:
  1. Reconnect the battery.
  2. Use the OBD-II scanner to clear the P0420 code from the ECM.
  3. Start the engine and allow it to reach operating temperature.