why does my Toyota Highlander check engine light come on with P0420 code

Solution

1. Preparation

• Gather tools and parts needed.
• Disconnect the battery to ensure safety while working on electrical components.
• Tools Required: OBD-II scanner, multimeter, infrared thermometer, socket set, and safety gloves.

2. Inspect and Replace Oxygen Sensors

1. Locate the upstream (pre-catalytic) and downstream (post-catalytic) oxygen sensors.
2. Disconnect the wiring harness from each sensor.
3. Using a socket set, remove the oxygen sensors from their respective positions.
4. Install new oxygen sensors, ensuring they are tightened to the manufacturer's specifications (usually 30-40 ft-lbs).
5. Reconnect the wiring harness to each sensor.

3. Inspect and Replace Catalytic Converter (if necessary)

1. If the catalytic converter is found to be faulty during diagnostics, prepare for replacement.
2. Remove the exhaust heat shield if necessary to access the catalytic converter.
3. Disconnect any bolts or clamps securing the catalytic converter to the exhaust system using a socket set.
4. Carefully remove the catalytic converter from the exhaust system.
5. Install the new catalytic converter, ensuring all bolts are tightened to the manufacturer's torque specifications (usually 25-30 ft-lbs).
6. Reinstall the exhaust heat shield if removed.

4. Clear Codes and Test

1. Reconnect the battery.
2. Use the OBD-II scanner to clear any fault codes.
3. Start the engine and let it run for a few minutes, monitoring for any check engine light reappearance.