how to fix P0420 Toyota Corolla E210 (2019-2024) without replacing the cat?

Solution

1. Preparation

• Gather necessary tools and parts.
• Ensure the vehicle is parked on a level surface and the engine is cool.
• Disconnect the negative battery cable to avoid electrical shorts.

2. Inspect and Clean Oxygen Sensors

• Tools Required: Oxygen sensor socket, cleaning solvent, wire brush
• Remove the downstream oxygen sensor using the oxygen sensor socket.
• Inspect the sensor for carbon buildup or damage. If dirty, clean with a wire brush and solvent.
• Reinstall the sensor and ensure it is tightened to manufacturer specifications (typically around 30 ft-lbs).

3. Repair Exhaust Leaks

• Tools Required: Socket set, exhaust sealant or new gaskets
• Inspect the exhaust system for leaks using visual inspection and the smoke test results.
• Tighten any loose bolts at exhaust joints.
• Replace any damaged gaskets or seals with new parts.
• Apply exhaust sealant if necessary to ensure a proper seal.

4. Reset the ECU

• Tools Required: OBD-II scanner
• Reconnect the negative battery cable.
• Use the OBD-II scanner to clear the P0420 code from the vehicle's computer.
• Start the engine and let it idle for a few minutes.

5. Test Drive

• Drive the vehicle under various conditions (city and highway) to allow the ECU to re-evaluate sensor data.
• Monitor for any reappearance of the P0420 code.