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

Solution

1. Preparation

• Gather all necessary tools and parts.
• Disconnect the negative battery terminal to prevent electrical shorts.
• Allow the exhaust system to cool if the vehicle has been running.

2. Inspect and Test Oxygen Sensors

• Tools Required: OBD-II scanner, multimeter.
• Remove the upstream (pre-catalytic) and downstream (post-catalytic) oxygen sensors using a socket wrench.
• Use the OBD-II scanner to monitor the voltage output of each sensor while the engine runs.
• A healthy upstream sensor should fluctuate between 0.1V and 0.9V, while the downstream should remain relatively steady.
• Replace any faulty sensors.

3. Inspect and Replace Catalytic Converter (if necessary)

• Tools Required: Socket set, torque wrench, exhaust gasket, penetrating oil.
• If the catalytic converter is determined to be faulty, loosen the exhaust clamps and disconnect the exhaust pipes.
• Remove the catalytic converter from its mounting brackets.
• Install the new catalytic converter with the provided gaskets, ensuring proper alignment.
• Torque the bolts to the manufacturer’s specifications (typically 30-50 ft-lbs).

4. Clear Codes and Test Drive

• Reinstall the oxygen sensors if removed, ensuring they are tightened properly.
• Reconnect the negative battery terminal.
• Use the OBD-II scanner to clear the P0420 code.
• Perform a test drive under various conditions to ensure the issue does not recur.