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

Solution

1. Preparation

• Tools Required: OBD-II scanner, multimeter, socket set, torque wrench, exhaust system jack stands.
• Ensure the vehicle is on a level surface and the engine is cool. Disconnect the battery to avoid any electrical issues during repair.

2. Inspect and Replace Oxygen Sensors

• Sub-steps:
  1. Locate the upstream and downstream oxygen sensors on the exhaust manifold and exhaust pipe, respectively.
  2. Disconnect the electrical connectors from both sensors.
  3. Use a socket wrench to remove the oxygen sensors.
  4. Install new oxygen sensors, applying anti-seize compound on the threads.
  5. Torque the sensors to the manufacturer’s specifications (typically around 30 lb-ft).
  6. Reconnect the electrical connectors to both sensors.

3. Inspect and Replace Catalytic Converter

• Sub-steps:
  1. Support the exhaust system with jack stands.
  2. Remove any heat shields or brackets securing the catalytic converter.
  3. Unbolt the catalytic converter from the exhaust manifold and the exhaust pipe. Use penetrating oil if bolts are rusted.
  4. Remove the old catalytic converter from the vehicle.
  5. Install the new catalytic converter, ensuring proper alignment with the exhaust system.
  6. Torque the mounting bolts to manufacturer specifications (typically 40 lb-ft).
  7. Reinstall any heat shields or brackets that were removed.

4. Reset Engine Control Module

• Sub-steps:
  1. Reconnect the vehicle battery.
  2. Use the OBD-II scanner to clear the P0420 code from the engine control module.
  3. Start the engine and allow it to idle for a few minutes to recheck the system.