how to fix P0420 code on Toyota Highlander Fourth Generation (2020-present)

Solution

1. Preparation

• Gather tools and parts required for the repair.
• Park the vehicle on a flat surface and engage the parking brake.
• Disconnect the negative battery terminal to ensure safety.

2. Inspect and Replace Oxygen Sensors

1. Locate the upstream and downstream oxygen sensors connected to the catalytic converter.
2. Using a socket wrench, carefully remove the upstream oxygen sensor and inspect it for damage.
3. If the sensor is faulty, replace it with a new one and torque it to the manufacturer's specification (usually around 30 ft-lbs).
4. Repeat the process for the downstream oxygen sensor.

3. Inspect the Catalytic Converter

1. Visually inspect the catalytic converter for any physical damage or signs of clogging.
2. If damage is present, remove the catalytic converter from the vehicle. This typically involves unbolting it from the exhaust pipe and the exhaust manifold.
3. Replace the catalytic converter with a new OEM or high-quality aftermarket part. Ensure all gaskets are replaced to prevent leaks.

4. Reinstall Components

1. Reattach any components that were removed during inspection or replacement, ensuring all bolts are tightened to the specified torque.
2. Reconnect the negative battery terminal.

5. Clear Codes and Test

1. Use the OBD-II scanner to clear the P0420 code from the vehicle's computer.
2. Start the engine and allow it to reach operating temperature.
3. Take the vehicle for a short test drive to ensure the check engine light does not reappear.