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

Solution

1. Preparation

• Gather all necessary tools and parts.
• Ensure the vehicle is parked on a level surface and the engine is cool.
• Disconnect the battery to avoid electrical shorts.

2. Inspect and Test 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 sensors.
  3. Using a multimeter, test the voltage output of both sensors while the engine is running. The upstream sensor should fluctuate between 0.1V and 0.9V, while the downstream sensor should be more stable (around 0.5V).
  4. If the upstream sensor is not functioning properly, replace it.

3. Inspect and Replace Catalytic Converter (if necessary)

• Sub-steps:
  1. If the catalytic converter is found to be damaged or if the oxygen sensors are functioning correctly, it may be necessary to replace the catalytic converter.
  2. Remove the exhaust pipe connections to the catalytic converter using a socket set.
  3. Unbolt the catalytic converter from its mounting brackets.
  4. Install the new catalytic converter by reversing the removal steps.
  5. Torque all bolts to the manufacturer’s specifications (refer to service manual for specific torque values).

4. Reconnect Battery and Clear Codes

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