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

Solution

1. Preparation

• Gather all necessary tools and parts before starting the repair.
• Disconnect the negative terminal of the battery to ensure safety.
• Raise the vehicle and secure it on jack stands for access to the exhaust system.

2. Inspect and Replace Oxygen Sensors

• Tools Required: O2 sensor socket, ratchet and extensions, penetrating oil.
• Locate the upstream and downstream oxygen sensors on the exhaust manifold and catalytic converter.
• Apply penetrating oil to the sensor threads and allow it to sit for a few minutes.
• Use the O2 sensor socket to remove the upstream sensor first, then the downstream sensor.
• Compare the old sensors to the new ones to ensure they match.
• Install the new oxygen sensors, tightening to the manufacturer's torque specification (typically around 30 lb-ft).

3. Examine and Replace the Catalytic Converter (if necessary)

• Tools Required: Socket set, torque wrench, gasket scraper.
• Inspect the catalytic converter for any physical damage, clogging, or rattling.
• If the catalytic converter is damaged or clogged, remove it by unbolting the flanges and disconnecting any hangers.
• Clean the mounting surfaces on the exhaust system to remove old gasket material.
• Install the new catalytic converter, ensuring a proper fit and sealing with a new gasket or exhaust sealant.
• Torque the bolts to the specified values (usually around 30-40 lb-ft), following the manufacturer's guidelines.

4. Reconnect Battery and Clear Codes

• Reconnect the negative terminal of the battery.
• Use the OBD-II scanner to clear the P0420 code from the ECM.

5. Test Drive the Vehicle

• Conduct a test drive under various conditions (stop-and-go, highway speeds) to ensure the issue is resolved.