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

Solution

1. Preparation

• Gather the necessary tools and parts.
• Disconnect the negative battery terminal to prevent electrical shorts.

2. Inspect and Replace Oxygen Sensors

• Tools Required: O2 sensor socket, torque wrench
• Sub-steps:
  1. Locate the upstream and downstream oxygen sensors in the exhaust system.
  2. Use the O2 sensor socket to carefully unscrew the sensors from their respective locations.
  3. Inspect the sensors for any signs of damage or contamination.
  4. Install new oxygen sensors, ensuring to torque them to the manufacturer’s specifications (typically around 30 lb-ft).

3. Check and Replace Catalytic Converter

• Tools Required: Socket set, possibly a torch for exhaust bolts
• Sub-steps:
  1. Locate the catalytic converter in the exhaust system.
  2. Remove the heat shield if applicable.
  3. Disconnect the exhaust pipes from the catalytic converter by removing the bolts or nuts (may require penetrating oil if rusted).
  4. Remove the catalytic converter from its mounts.
  5. Install the new catalytic converter, ensuring proper alignment with the exhaust system.
  6. Reattach the exhaust pipes and torque the bolts to the manufacturer's specifications.

4. Clear Codes and Test Drive

• Sub-steps:
  1. Reconnect the negative battery terminal.
  2. Use an OBD-II scanner to clear the P0420 code.
  3. Test drive the vehicle under varied conditions for at least 20 minutes to verify that the check engine light does not reappear.