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

Solution

1. Preparation

• Gather necessary tools and parts.
• Disconnect the negative terminal of the battery to prevent electrical shorts.
• Allow the engine to cool down before starting work.

2. Inspect and Replace Oxygen Sensors

• Tools Required: O2 sensor socket, ratchet, torque wrench
• Remove the upstream oxygen sensor:
  • Locate the sensor in the exhaust manifold or pipe.
  • Use the O2 sensor socket to unscrew the sensor.
• Install the new upstream oxygen sensor:
  • Apply anti-seize compound to the threads of the new sensor.
  • Torque to the manufacturer's specification (usually around 30 ft-lbs).
• Repeat the process for the downstream oxygen sensor if necessary.

3. Inspect and Replace Catalytic Converter

• Tools Required: Socket set, jack and jack stands, exhaust pipe cutter (if necessary), new gaskets
• Raise the vehicle with a jack and secure it with jack stands.
• Remove the exhaust heat shield if applicable.
• Disconnect the exhaust pipes from the catalytic converter:
  • Use a socket set to unbolt the connections.
  • Cut the exhaust pipe if it is too corroded to remove.
• Remove the catalytic converter:
  • Unbolt it from the exhaust manifold and any mounting brackets.
• Install the new catalytic converter:
  • Position it correctly and secure with the bolts.
  • Replace gaskets as needed to prevent leaks.
• Re-connect the exhaust pipes and torque bolts to the manufacturer's specifications.

4. Clear Codes and Test Drive

• Reconnect the battery terminal.
• Use an OBD-II scanner to clear the P0420 code.
• Start the engine and let it idle for a few minutes.
• Take the vehicle for a test drive to ensure the check engine light does not reappear.