what causes the P0420 code in my Toyota Highlander and how to fix it

Solution

1. Preparation

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

2. Inspect and Replace O2 Sensors

• Sub-steps:
  1. Locate the upstream and downstream oxygen sensors on the exhaust system.
  2. Use an O2 sensor socket to remove the sensors.
  3. Inspect the threads and wiring of the sensors for damage.
  4. Install new O2 sensors, applying anti-seize compound on the threads if needed.
  5. Torque the sensors to the manufacturer's specifications (usually around 30 Nm).

3. Inspect and Replace Catalytic Converter

• Sub-steps:
  1. Remove the heat shields covering the catalytic converter if applicable.
  2. Disconnect the exhaust pipes leading to and from the catalytic converter.
  3. Remove any mounting bolts or clamps securing the catalytic converter.
  4. Inspect the old catalytic converter for signs of clogging or damage.
  5. Install the new catalytic converter, ensuring proper alignment and sealing.
  6. Reattach exhaust pipes, torqueing bolts to the specified settings.

4. Reconnect Battery and Clear Codes

• Sub-steps:
  1. Reconnect the battery terminals securely.
  2. Use an OBD-II scanner to clear the P0420 code.
  3. Start the engine and allow it to idle for a few minutes to ensure normal operation.