how to fix P0420 code on my 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 battery to prevent electrical shorts.

2. Inspect and Replace Oxygen Sensors

• Tools Required: O2 sensor socket, wrench set, penetrating oil.
• Sub-steps:
  1. Locate the upstream and downstream oxygen sensors (the upstream is typically before the catalytic converter).
  2. Apply penetrating oil on the sensor threads to ease removal.
  3. Disconnect the electrical connectors from both sensors.
  4. Use the O2 sensor socket to remove the old sensors.
  5. Install new oxygen sensors, tightening them to the manufacturer’s specifications (usually 30-45 Nm).
  6. Reconnect the electrical connectors to the new sensors.

3. Inspect and Replace Catalytic Converter

• Tools Required: Socket set, torque wrench, exhaust pipe cutter (if necessary).
• Sub-steps:
  1. Inspect the catalytic converter for any signs of damage, clogging, or excessive heat discoloration.
  2. If replacement is necessary, disconnect the exhaust pipes by removing the bolts or clamps securing them.
  3. Remove the old catalytic converter from the exhaust system.
  4. Install the new catalytic converter, ensuring proper alignment with the exhaust pipes.
  5. Tighten all bolts to the specified torque (typically 30-40 Nm) to prevent leaks.

4. Reconnect Battery and Reset the Check Engine Light

• Sub-steps:
  1. Reconnect the negative battery terminal.
  2. Use the OBD-II scanner to clear the P0420 code.

5. Test Drive

• Take the vehicle for a test drive to ensure the repair was successful and monitor for any reappearance of the check engine light.