how to fix a P0420 code on my Toyota Corolla E140 (2006-2013) after replacing the cat

Solution

1. Preparation

• Gather all necessary tools and parts for the repair.
• Disconnect the negative terminal of the battery.
• Allow the engine to cool down before starting work.

2. Inspect O2 Sensors

• Tools Required: OBD-II scanner, multimeter
• Remove the upstream (pre-cat) and downstream (post-cat) O2 sensors from the exhaust system.
• Inspect the O2 sensor wiring and connectors for damage or corrosion.
• Test the sensors using a multimeter:
  • Set the multimeter to voltage mode.
  • Start the engine and let it idle.
  • Measure the voltage output from the upstream sensor; it should oscillate between 0.1V to 0.9V.
  • Measure the downstream sensor; it should show a more stable voltage if the catalytic converter is functioning properly.
• Replace any faulty O2 sensors.

3. Repair Exhaust Leaks

• Tools Required: Exhaust sealant, gasket maker, wrench set
• Inspect the exhaust system for leaks, focusing on joints and connections.
• Repair any leaks found using exhaust sealant or by replacing gaskets.
• Ensure all connections are tight and secure.

4. Clear Error Codes

• Tools Required: OBD-II scanner
• After repairs, use the OBD-II scanner to clear the P0420 code from the vehicle’s computer.
• Reconnect the negative battery terminal.

5. Test Drive

• Take the vehicle for a test drive under various driving conditions to ensure the issue has been resolved.
• Monitor the OBD-II system for any reoccurrence of the P0420 code.