how to fix P0420 code in my Honda Civic 10th Generation (2016-2021)

Solution

1. Preparation

• Gather all necessary tools and parts.
• Disconnect the battery to prevent any electrical issues during the repair.
• Allow the engine to cool down before proceeding.

2. Inspect and Replace Oxygen Sensors

• Tools Required: O2 sensor socket, ratchet, torque wrench.
• Sub-steps:
  1. Locate the upstream (pre-catalytic) and downstream (post-catalytic) oxygen sensors.
  2. Disconnect the electrical connectors from both sensors.
  3. Use the O2 sensor socket to remove the sensors from the exhaust manifold and catalytic converter.
  4. Install new oxygen sensors in the same locations, tightening to the manufacturer’s specified torque (usually around 30 lb-ft).
  5. Reconnect the electrical connectors securely.

3. Inspect and Replace Catalytic Converter

• Tools Required: Socket set, torque wrench, cutting tool (if needed for old converter), gasket scraper.
• Sub-steps:
  1. Safely raise the vehicle and support it with jack stands.
  2. Remove the exhaust heat shields if applicable.
  3. Disconnect the exhaust pipes from the catalytic converter (may require cutting if rusted).
  4. Remove the catalytic converter by unscrewing the mounting bolts.
  5. Clean the mounting surfaces using a gasket scraper.
  6. Install the new catalytic converter, ensuring proper alignment and secure all bolts to the specified torque (typically 30 lb-ft).
  7. Reattach exhaust pipes and any heat shields removed earlier.