how to fix P0420 catalyst efficiency below threshold in Toyota Highlander Fourth Generation (2020-pr...

Solution

1. Preparation

• Tools Required: OBD-II scanner, multimeter, basic hand tools, jack and jack stands.
• Ensure the vehicle is parked on a level surface and the engine is cool.
• Disconnect the battery to avoid any electrical shorts.

2. Inspect and Replace Oxygen Sensors

• Sub-steps:
  1. Locate the upstream (pre-catalytic) and downstream (post-catalytic) oxygen sensors.
  2. Disconnect the electrical connectors from both sensors.
  3. Using a socket wrench, remove the sensors from the exhaust system.
  4. Install new oxygen sensors, tightening them to the manufacturer's specifications (usually around 30 ft-lbs).
  5. Reconnect the electrical connectors.

3. Inspect and Replace the Catalytic Converter

• Sub-steps:
  1. Safely lift the vehicle using a jack and secure it with jack stands.
  2. Locate the catalytic converter and inspect it for physical damage or excessive rust.
  3. Disconnect the exhaust pipes at both ends of the catalytic converter, using appropriate tools.
  4. Remove the catalytic converter from its mounting brackets and replace it with a new one that meets OEM specifications.
  5. Reconnect the exhaust pipes and ensure all bolts are tightened to the specified torque (typically around 25-30 ft-lbs).

4. Clear Codes and Test Drive

• Sub-steps:
  1. Reconnect the battery.
  2. Use the OBD-II scanner to clear the P0420 code from the vehicle's computer.
  3. Start the engine and allow it to reach operating temperature.
  4. Perform a test drive under various driving conditions to ensure the check engine light does not reappear.