how to diagnose P0420 code in my Toyota Corolla E170 (2013-2019) and fix the issue?

Solution

1. Preparation

• Gather tools and parts needed for the repair.
• Disconnect the battery before starting any work on the vehicle.
• Allow the engine to cool down.

2. Inspect and Replace Oxygen Sensors

1. Locate the upstream (pre-catalytic converter) and downstream (post-catalytic converter) oxygen sensors.
2. Use a socket wrench to remove the oxygen sensors from their respective locations.
3. Inspect the sensors for signs of damage or excessive carbon buildup. Clean or replace as necessary.
4. If replacing, install the new sensors by threading them into their respective ports and tightening to the manufacturer's specifications (typically 30-40 Nm).
5. Reconnect the wiring harnesses to the new sensors.

3. Inspect and Replace the Catalytic Converter

1. If the oxygen sensors are functioning properly, proceed to inspect the catalytic converter for damage.
2. Remove any heat shields covering the catalytic converter if applicable.
3. Use a socket set to unbolt the catalytic converter from the exhaust system (pay attention to any gaskets that may need replacing).
4. Inspect the interior of the catalytic converter for blockage or signs of melting.
5. Install a new catalytic converter by reversing the removal process, ensuring proper gasket placement and tightening bolts to the manufacturer's torque specifications.

4. Reset the OBD-II System

1. Reconnect the battery after completing repairs.
2. Use an OBD-II scanner to clear any stored trouble codes from the system.