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

Solution

1. Preparation

• Gather all necessary tools and parts.
• Ensure the vehicle is parked on a level surface and the engine is cool.
• Disconnect the battery by removing the negative terminal.

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 upstream oxygen sensor. Torque specification for installation: 30 lb-ft (41 Nm).
  4. Repeat for the downstream oxygen sensor if necessary.
  5. Install the new oxygen sensors, ensuring to use anti-seize compound on the threads if required.

3. Inspect and Replace the Catalytic Converter

• Tools Required: Socket set, torque wrench, gasket scraper, exhaust sealant
• Sub-steps:
  1. Locate the catalytic converter in the exhaust system.
  2. Check for any physical damage, such as dents or holes, and signs of overheating.
  3. Remove the bolts securing the catalytic converter to the exhaust manifold and exhaust pipe using a socket set.
  4. Carefully detach the catalytic converter from the exhaust system.
  5. Clean the mating surfaces on the exhaust manifold and pipe with a gasket scraper.
  6. Install the new catalytic converter, ensuring proper alignment.
  7. Torque the bolts to the specified value, usually around 40-50 lb-ft (54-68 Nm) depending on the model.