how to fix P0420 in Honda Accord Eleventh Generation (2023-present) after replacing the cat?

Solution

1. Preparation

• Tools Required: OBD-II scanner, multimeter, socket set, torque wrench, smoke tester.
• Safety Warnings: Disconnect the battery before working on electrical components. Allow the exhaust system to cool before inspection.

2. Inspect and Replace Oxygen Sensors

• Sub-steps:
  1. Locate the upstream (pre-catalytic) and downstream (post-catalytic) oxygen sensors.
  2. Disconnect the electrical connectors from both sensors.
  3. Use a socket wrench to remove the old oxygen sensors.
  4. Install new oxygen sensors and torque to manufacturer specifications (typically around 30 Nm).
  5. Reconnect the electrical connectors securely.

3. Check and Repair Exhaust Leaks

• Sub-steps:
  1. Use a smoke tester to identify any leaks in the exhaust system.
  2. Repair any leaks found using exhaust sealant or by replacing damaged pipes or gaskets.
  3. Ensure all connections are tight and free from corrosion.

4. Clear Error Codes

• Sub-steps:
  1. Reconnect the battery if it was disconnected.
  2. Use the OBD-II scanner to clear the P0420 code from the vehicle’s computer.
  3. Start the engine and let it reach operating temperature.