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

Solution

1. Preparation

• Gather tools and parts before starting the repair.
• Ensure the vehicle is parked on a level surface with the parking brake engaged.
• Allow the engine to cool down completely before starting work on the exhaust system.

2. Inspect and Replace Oxygen Sensors

1. Locate the oxygen sensors: Identify the upstream (pre-catalytic converter) and downstream (post-catalytic converter) oxygen sensors.
2. Disconnect the battery: Disconnect the negative terminal to prevent electrical shorts.
3. Remove the old sensors: Use an oxygen sensor socket to unscrew the sensors from their respective locations.
4. Install the new sensors: Apply anti-seize compound on the threads of the new sensors, then install them and torque to the manufacturer's specifications (typically around 30 lb-ft).
5. Reconnect the battery: Reattach the negative terminal.

3. Inspect and Replace the Catalytic Converter

1. Remove the exhaust components: If the catalytic converter is faulty, remove it by loosening the bolts and separating it from the exhaust pipes (use a socket set and possibly a breaker bar).
2. Inspect the catalytic converter: Check for signs of physical damage, melting, or clogging.
3. Install the new catalytic converter: Position the new catalytic converter and secure it in place. Torque the bolts to the manufacturer's specifications (usually around 30-40 lb-ft).
4. Reconnect any disconnected exhaust components: Ensure all parts are secure and aligned properly.

4. Clear the Codes

1. Use an OBD-II scanner: Connect the scanner to the vehicle's diagnostic port.
2. Clear the P0420 code: Follow the scanner instructions to erase the trouble codes from the ECM.

5. Test Drive

1. Start the vehicle: Allow it to idle and check for any exhaust leaks.
2. Take a test drive: Drive the vehicle under various conditions to ensure that the check engine light does not reappear and the vehicle operates smoothly.