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

Solution

1. Preparation

• Gather necessary tools and parts.
• Disconnect the negative battery terminal to avoid electrical shorts.
• Allow the vehicle to cool down if the engine has been running.

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. Remove the upstream oxygen sensor using the O2 sensor socket.
  3. Install the new upstream oxygen sensor and torque to manufacturer's specifications (typically around 30 ft-lbs).
  4. Repeat the process for the downstream oxygen sensor if it is also faulty.

3. Inspect and Replace Catalytic Converter

• Tools Required: Socket set, torque wrench, exhaust hanger removal tool.
• Sub-steps:
  1. Remove any heat shields or brackets holding the catalytic converter in place.
  2. Disconnect the exhaust pipes from the catalytic converter, using penetrating oil if necessary to loosen rusted bolts.
  3. Inspect the catalytic converter for blockages or physical damage.
  4. Install the new catalytic converter by reversing the removal procedure, ensuring all bolts are torqued to the specified values (usually around 30-40 ft-lbs).
  5. Reinstall heat shields and brackets as necessary.

4. Clear Codes and Test

• Tools Required: OBD-II scanner.
• Sub-steps:
  1. Reconnect the negative battery terminal.
  2. Use the OBD-II scanner to clear the P0420 code.
  3. Start the engine and allow it to reach operating temperature.
  4. Take the vehicle for a test drive to ensure the check engine light does not reappear.