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

Solution

1. Preparation

• Gather tools and parts required for the repair.
• Safety gear: gloves and safety glasses.
• Disconnect the battery to prevent electrical issues during repairs.

2. Inspect and Replace Oxygen Sensors

1. Locate the upstream and downstream oxygen sensors on the exhaust system.
2. Disconnect the electrical connectors from both sensors.
3. Use an oxygen sensor socket to remove the sensors from the exhaust system.
4. Install the new oxygen sensors by threading them into place; ensure they are tightened to manufacturer specifications (typically around 30 lb-ft).
5. Reconnect the electrical connectors to the new sensors.

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

1. Remove the exhaust heat shield (if applicable) by unscrewing the bolts.
2. Use a socket set to unfasten the bolts securing the catalytic converter to the exhaust manifold and exhaust pipe.
3. Carefully remove the catalytic converter from the vehicle. Inspect for physical damage or clogging.
4. Install the new catalytic converter, ensuring proper alignment and sealing surfaces.
5. Torque the bolts to the manufacturer's specifications, typically around 25 lb-ft for exhaust components.

4. Reconnect Battery and Clear Codes

1. Reconnect the negative battery terminal securely.
2. Use an OBD-II scanner to clear the P0420 code from the vehicle’s computer.