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

Solution

1. Preparation

• Gather tools and parts.
• Disconnect the negative battery terminal to prevent electrical shorts.
• Ensure the vehicle is on a level surface and secure it with jack stands if needed.

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 wiring harness from each oxygen sensor.
  3. Use the O2 sensor socket to remove the sensors from the exhaust pipe.
  4. Install new oxygen sensors, tightening them to the manufacturer's specification (usually around 30-35 lb-ft).
  5. Reconnect the wiring harness.

3. Inspect and Replace Catalytic Converter (if necessary)

• Tools Required: Socket set, ratchet, exhaust gasket, torque wrench.
• Sub-steps:
  1. Remove any heat shields or covers protecting the catalytic converter.
  2. Unbolt the catalytic converter from the exhaust manifold and the exhaust pipe, using a socket set.
  3. Inspect the mounting flanges for damage; replace gaskets as necessary.
  4. Install the new catalytic converter, ensuring the bolts are tightened to the manufacturer’s specifications (typically around 30-35 lb-ft).
  5. Reinstall any heat shields or covers that were removed.

4. Clear Codes and Test

• Tools Required: OBD-II scanner.
• Sub-steps:
  1. Reconnect the negative battery terminal.
  2. Use an OBD-II scanner to clear the P0420 code from the system.
  3. Start the engine and allow it to reach operating temperature.
  4. Take the vehicle for a test drive to see if the check engine light returns.