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

Solution

1. Preparation

• Gather necessary tools and parts.
• Ensure the vehicle is parked on a level surface and the ignition is off.
• Disconnect the battery to prevent electrical shorts.

2. Inspect and Replace Oxygen Sensors

• Tools Required: O2 sensor socket, torque wrench, multimeter.
• Using the O2 sensor socket, remove the pre-cat oxygen sensor from the exhaust manifold.
• Inspect the sensor for damage or contamination; replace if necessary.
• Install the new sensor and torque to manufacturer's specification (typically around 30 lb-ft).
• Repeat the process for the post-cat oxygen sensor.

3. Inspect and Replace Catalytic Converter

• Tools Required: Socket set, torque wrench, exhaust pipe cutter (if needed).
• Raise the vehicle using jack stands and remove any underbody shields.
• Disconnect the exhaust pipes from the catalytic converter using the socket set.
• Remove the catalytic converter from its mounting points.
• Inspect the old converter for signs of damage or clogging.
• Install the new catalytic converter, ensuring all connections are tight and torqued to specifications.
• Reattach underbody shields and lower the vehicle.

4. Clear Codes and Test Drive

• Reconnect the battery and clear any diagnostic trouble codes using the OBD-II scanner.
• Start the engine and allow it to reach operating temperature.
• Take the vehicle for a test drive under various conditions to ensure the P0420 code does not return.