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

Solution

1. Preparation

• Gather all necessary tools and parts.
• Disconnect the negative battery terminal to prevent any electrical issues.
• Raise the vehicle using a jack and secure it on jack stands for safe access.

2. Inspect and Test Oxygen Sensors

• Tools Required: OBD-II scanner, multimeter.
• Remove the upstream oxygen sensor (before the catalytic converter) using a socket wrench.
• Test the voltage output of the sensor while the engine is running; it should fluctuate between 0.1V and 0.9V.
• If faulty, replace the oxygen sensor with a new one, ensuring the connector is secure.

3. Examine the Catalytic Converter

• Tools Required: Socket set, pry bar (if needed).
• Inspect the catalytic converter for physical damage or discoloration.
• If no visible issues, perform an exhaust temperature test. The temperature should be significantly higher after the catalytic converter than before; a small difference suggests a failing catalytic converter.
• If the catalytic converter is determined to be inefficient, remove it from the exhaust system by loosening the bolts and carefully separating it.

4. Replace the Catalytic Converter

• Parts Required: New catalytic converter.
• Install the new catalytic converter by aligning it with the exhaust system.
• Tighten the bolts to the manufacturer’s specified torque (check the service manual for the exact torque value).
• Reconnect the oxygen sensors to their respective locations.

5. Reconnect Battery and Clear Codes

• Reconnect the negative battery terminal.
• Use the OBD-II scanner to clear the P0420 code from the vehicle's computer.
• Perform a test drive to monitor for any reoccurrence of the check engine light.